Validators between classical and professional usage

April 29, 2010

Introduction
Web2py validators work at the form level, not on the database level
It's recommended though to make both validation at the form level and database level.

  • You can add validators whereever you want but you’ve to pay attention for the logic.
    you can make:

    
    db.define_table('my_table', Field('my_f', requires=[..]))
    # or  inside the same model after the definition of the table :
    db.define_table('my_table', Field('my_f'))
    db.my_table.my_f.requires = [....]
     # you may even do this in your controller
    db.my_table.my_f.requires = [....]  
    form = SQLFORM(db.my_table)
    ......
    

    Things to note though that making adding validators after defining the table or before defining the form in your controller is that in those 2 particular situations, you’re really overriding any other validators on this table field defined in the model, either within the table definition or after it .

    db.define_table('my_table', Field('my_f', requires=[set_no_1]))
    db.my_table.my_f.requires = [set_no_2]  
    

    In the example above, set_no_2 of validators is the one that will actually work.

    To overcome this situation, you may make something like:

    db.define_table('soso', Field('lolo'), Field('moon', requires=[IS_NOT_EMPTY()]))
    db.soso.moon.requires.append(IS_NOT_IN_DB(db, db.soso.moon))
    

    Wow !!! then you can append to the list from anywhere and it will work.

  • Now one can wonders , so what’s the catch ?

  • The catch is that making something like :
    db.my_table.my_f.requires = [IS_IN_DB(...)]
    

    will prevent this field from being represented as a combo box, for this to be achieved you’ve not to make a list

    db.my_table.my_f.requires = IS_IN_DB(...)
    

    in this case you can’t add other validators and any trial to override the validators will ruin the combo box widget.

  • The good news is that there’s a solution 😀 which is ‘using widgets’, look ath this piece of code:
    b.define_table('soso', Field('lolo'), Field('moon', widget=SQLFORM.widgets.options.widget, requires=[IS_IN_DB(db, db.country.name), IS_UPPER()]))
    

    What I did was to force the usage of the options widget, and in this case it will work fine and the other validator will also work, and the value to be entered in database is the the uppercase value of the one you’ve chosen.
    WARNING: IS_IN_DB() MUST be the first in the list, for this to work.


  • IS_IN_DB() and IS_NOT_IN_DB() logical issue

    when using either of the 2 validators, you have to take care of something , which is that you can’t do something like:

    db.define_table('country', Field('name', requires=IS_NOT_IN_DB(db, db.country.name)))
    

    what you want to do is making the country name unique, and not to allow duplication.
    Let’s look more precisely about what you’ve done above.
    requires=IS_NOT_IN_DB(db, db.country.name)
    can you really use db.country.name before the country table is really defined ? You can’t and thus in this case you’ve to move your validation to be after the table definition , something like:

    db.define_table('country', Field('name'))
    db.country.name.requires= IS_NOT_IN_DB(db, db.country.name)
    

    IS_IN_DB() or IS_IN_DB() classical usage
    The same logic goes for both, so I’ll concentrate on one the other will be almost the same, except for the functionality ofcourse.

    db.define_table('category', Field('name'))
    db.define_table('recipe', Field('category', 'reference category'))
     db.recipe.category.requires=IS_IN_DB(db,'category.id','category.name')
       # or
    db.recipe.category.requires=IS_IN_DB(db,db.category.id,'category.name') 
    

    The parameters are:

    • a set of records
    • ‘category.id’ (string) or db.category.id (not a string) describes how the field will be represented in the
      database [this is the value that will be actually sent when accepting a SQLFORM that is using this table]
    • ‘category.name’ describes how the field will be represented to the
      user [Just a representation] and you’ll end up with a combo box displaying the name while accepting the form will send the id to database.
      name is a valid field name in the same table.
    # model
    db.define_table('table_one', Field('name'))
    db.define_table('table_two',Field('a', requires=IS_IN_DB(db, 'table_one.id', '%(name)s')))
    
    # controller
    def index():
        form = SQLFORM(db.table_two)
        if form.accepts(request.vars, session):       
            print form
        return dict(form=form)
    

    supposing table_one has only one record {id=1, name=’hamdy’}
    the form will display a drop down box with one item “hamdy”
    but upon accepting form the id (1) will actually be stored in db

    print form will give you something like:

    <form action="" enctype="multipart/form-data" method="post">
    .........................................................
    <select class="string" id="table_two_a" name="a"><option value=""></option><option value="1">hamdy</option></select></form>
    .........................................................
    

    In fact to be honest what really got to the database in table_two is just an id.
    To make things more professional you’ve to make this id refer to the actual record in tabl_one not just an id.
    To achieve this and test it , do something like:

    # add to your model :
    db.define_table('table_three',Field('a', 'reference table_one', requires=IS_IN_DB(db, 'table_one.id', '%(name)s')))
    
    # controller
    def index():
        form = SQLFORM(db.table_three)
        if form.accepts(request.vars, session):       
            print form
        return dict(form=form)
    

    Now when you go to the appadmin interface to check you database,
    you’ll find that the id in the record is a link to the actual record in the other table and obviously this’s what you wanted from the beginning a foreign key.
    In this case you can add to the field ‘a’ in table_one : ondelete=’CASCADE’ so that when the record in a deleted , all other records in other tables referencing it will be deleted automatically and this is a thing you WILL ALWAYS need, otherwise you’ll suffer a severe headache trying to trace unused records and delete them manually
    in separate database queries.


    IS_IN_DB() professional usage

    • making something like:
      db.define_table('table_two',Field('a', requires=IS_IN_DB(db(db.table_one.name.like('h%')), 'table_one.name')))
      

      you’ll get a combo box with names in your table that starts with ‘h’ .
      choosing one of them and submitting the form will submit its id
      you may even do something like:

      db.define_table('table_two',Field('a', requires=IS_IN_DB(db(db.table_one.name.like('h%')),                       'table_one.id', 'Name: %(name)s, id: %(id)s')))
      

      Note that :

       'Name: %(name)s, id: %(id)s')
      

      is just a string that looks similar to ‘Name:….., id:….’ :

      Name:hamdy, id:1
      Name:aaaa, id:2

      and as I said before, submitting it will submit the id .

      The bottom line here :

      • You just can play with the presentation [how field looks like for user] while the data that will enter the database is different.
      • You can use a query inside IS_IN_DB(query, presentation) and the query is just logically representing a WHERE clause of database query

    Another Professional usage for IS_IN_DB()

  • How to use IS_IN_DB() to make records entered by a user are unique
    but in the same time those records can be entered again but by another user ?
    • Using the web2py example, we have 2 tables, “owners” and “dogs”. The “dogs” table has a many 2 one relation to owners.
      How can I create a constraint/ validator that allows the owner to give
      his dogs unique names? I cannot use IS_NOT_IN_DB because it is is
      database wide, I would like to have duplicate names in the table, but
      not allow duplicate names for a given user. Example, an owner called
      Voltron can have 2 dogs called “skipper” and “lassie” but not
      “skipper” and “skipper”, but another owner called ‘Optimus Prime’ could
      also have a dog called “skipper” or “lassie”
      Was that clear? Any ideas?

      IS_NOT_IN_DB(db(db.dog.owner==owner_id),db.dog.name) 
      

    What I wanted to show you in the previous section is that you can do things using many ways and to ensure you understand the :
    IS_IN_DB() and IS_NOT_IN_DB() and that they can be passed (db) as the first parameter or passed a set of records using db(my_query)
    then the 2nd argument is a database field that either written as :
    'my_table.my_field' as a string or db.my_table.my_field


    Yet another professional usage for IS_IN_DB()

    How to make a data set of some records in a table with appropriate permissions then requires user to choose among them ?

    # Model
    db.define_table('company', ......)
    db.define_table('news',
                    Field('company_id', 'reference company'),                 
                    .....................   
                    migrate=migrate
                    )
    
    db.news.company_id.requires = IS_IN_DB(db(auth.accessible_query(Permissions.OWNER,db.company,auth.user.id)), db.company.name) if auth.is_logged_in() else None
    # db.company.name -> to display company name instead of company id
    

    If you’ve a user who is a company OWNER or several companies OWNER
    then when he ever wants to enter news for one or more companies that he owns, the form should allow him to choose among those companies and make him choose which one to enter news for.

    db(auth.accessible_query(Permissions.OWNER,db.company,auth.user.id
    

    returns records from company db.table that the current logged in user [auth.user.id] has OWNER permission on them
    In fact permissions are set based on groups so what this code really does is to check whether the current user belongs to a group that has OWNER permissions on some records of the table db.company and return those records

    the reason for requires=….. if auth.is_logged_in() else None is that when a user is not logged in the auth.user is not there so it’s None, and that causes the application to fail because auth.user.id is not there [None has no id attribute] so simply I made that simple check knowing that this table is used for forms that requires a user to login.


    Now time for another neat trick that web2py permits
    In fact, you can make validation on a field based on another’s field’s value that is submitted from a form !!! on the fly.
    Consider the following example:

    db.define_table('my_table', Field('category', requires=IS_IN_SET(['url_required', 'url_not_required'
                                ]
                       )
                                 ),
                                 
                           Field('url', requires = IS_EMPTY_OR(IS_URL()) if request.vars.category == 'url_not_required' else IS_URL()
                                 ))
    

    Great .. .right ? 😀

  • In fact IS_IN_SET can be a list of say … records ids and in the same time having labels [aliases] to be human readable
    so making something like:

    db.define_table('my_table', Field('toto', requires = IS_IN_SET([1, 2, 3], labels=['one', 'two', 'three'])))
    

    will yield a dropdown menu with the values[ ‘one’, ‘two’, ‘three’] but in fact what is being sent to database is the integers (ids) [1, 2 or 3]

  • You can even use IS_IN_LIST() with dates, … say for example you’ve a field of type ‘datetime’ then you want users to enter specific dates in it, so you can do something like:
    db.define_table('my_table', Field('date', 'datetime'))
    db.my_table.date.requires=IS_IN_SET([
      datetime.date(1492,10,12),
      datetime.date(1492,11,02),
      datetime.date(1492,11,27)])
    

    Now user will get a drop down menu of the specified dates .


  • Another neat usage for IS_EMPTY_OR() or IS_NULL_OR() [they’re the same] is when you have a table with a field that refers to another table.
    in this particular situation the referencing field must have a value that is equivalent to an existing record id on the referenced table.
    and because it’s difficult to remember the ids or even to know it, you should use IS_IN_DB() validator to have a drop down menu to choose from it . And as you all know, you can format the value in drop down menu to display names instead of ids and what is really going to be sent to server and database is the id.

    db.define_table('cat', Field('category'))
    db.define_table('my_table', Field('category', 'reference cat', requires=IS_IN_DB(db, db.cat.id)))
    # use 'reference cat' or db.cat without single quotes
    

    Now what if you want to have the db.my_table.category set to a category id or if there’s no category you just want Null in this database field or you want just a specific default id to be stored if user let this field empty.
    In this case you use : IS_EMPTY_OR(….., null=) so I can have something like :

    # controller
    def index():
       form = SQLFORM(db.my_table)
       if form.accepts(request.vars, session):
           response.vars = T('yes')
       return dict(form=form)
    
    #model
    db.define_table('cat', Field('category'))
    db.define_table('my_table', Field('category', 'reference cat', requires=IS_EMPTY_OR(IS_IN_DB(db, db.cat.id), null=None)))
    

    In this case you can just let this field empty and not to choose a category and in this case will be stored in this field.
    If you want something other than such as a default category id, you can use :

    requires=IS_EMPTY_OR(IS_IN_DB(db, db.cat.id), null=1))
    # 1 should be valid record in db.cat
    <strong>Warning:</strong> if the value assigned yo null= dosn't exist , you 'll get an error trying to access database table via appadmin interface, it should be a valid record id in the referenced table.
    
    

    oh, don’t forget to check my discussion about the IS_EMPTY_OR() validator in Web2py Zen


  • How could I get rid of some validators that I don’t like in some actions
    [controller functions] ?

    anywhere in your action before defining the SQLFORM, just do:

    db.my_table.my_field.requires=[] 
    

  • How could one validate against a set of translated values?

    you do it the normal way:

    db.define_table('table_two_two',Field('a', 'string', requires=IS_IN_SET([T('v'), T('d')])))
    #requires=[IS_IN_SET(..)] -&gt; No combobox
    #requires=[IS_IN_SET(..)] -&gt; combobox
    

    Date & Time Validators

    Now we've IS_DATE, IS_TIME, IS_DATE_TIME
    
    db.define_table('a', Field('date', 'datetime'))
    db.a.date.requires=IS_DATETIME('%Y-%m-%d %H:%M:%S-%p', error_message=...)
    

    and the date field b will be processed in the desired format, specified by the custom format string that you can edit as you like :

    ('%Y-%m-%d %H:%M:%S-%p'
    

    For Numbers you use

    IS_INT_IN_RANGE(min,max)
    

  • For Telephones:
    you may use something like :

    IS_MATCH(&quot;^1+\d{3}\-?\d{3}\-?\d{4}$&quot;)
    # or for european something like
    IS_MATCH(&quot;^\+?[\d\-]*$&quot;) 
    
  • How do I validate a number that must always consist of 5 numerals including numbers starting with a 0? Here are examples are 12345, 01234, 89765. I used IS_INT_IN_RANGE but the numerals that start with 0 did not validate. ?

    You need to store as ‘string’ with length=5 and require

    IS_MATCH('^\d{5}$') 
    

    Telephone numbers should be stored as strings otherwise numbers starting with 0 will be treated as octal numbers.


  • validation not working on FORM field why?

    Now when talking about FORM validation it’s the same as the SQLFORM validation , though you’ve to notice something :
    Take care and give form field a name in order for validation to work
    ex:

    # validation here won't work, although the form submission seems to work just fine
    form = FORM(INPUT(_type='text', requires=IS_LENGTH(minsize=3, maxsize=8)),
                    INPUT(_type='submit')
                    )
        if form.accepts(request.vars, session):
            response.flash = T('hey')
        return dict(form=form)
    

    In order for the previous example to work, field needs to have a name
    so that requst.vars contains request.vars.field_name and the validation works.
    So you need change the form definition into something like:

    
    form = FORM(INPUT(_name='name', _type='text', requires=IS_LENGTH(minsize=3)),
                    INPUT(_type='submit')
                    )
    

  • You can use IS_LIST_OF() validator to validate a list of values

  • Q: I’ve my own function that does something complex and I want to use it for values submitted from a form to process that data and make some operation on it before actually being saved to database.
    What can I do?

    Ans:

    Suppose you’ve a function like:

    def my_owsome_func(x):
        return return x.replace('-', '_')
    

    Now I’m having in my model:

    db.define_table('my_table', Field('my_url', requires=IS_URL()))
    

    and in my controller:

     form = SQLFORM(db.my_table)
        if form.accepts(request.vars, session):
            response.flash = T('yes')
        return dict(form=form)
    

    Now I want when user inputs a URL, the my_owsome_func() processes the URL before actually saved into database then replace every occurrence of ‘-‘ with ‘_’.

    Think a little … what is the thing that processes data before actually being saved into database ?
    Yes … Validators
    Now if I were able to use my_owsome_func() in a validator, this would be awsome ..!!!!
    Yes you can :
    you can make your custom validator like:

    from gluon.validators import Validator
    class MY_CUSTOM_VALIDATOR(Validator):
        def __init__(self, f):
            self._f = f
        def __call__(self, value):
            return (self._f(value), None)
    

    as you can see a typical validator should (but not required to) extend the Validator class in gluon.validators .
    gluon.validators.Validator includes a formatter() function that you might need in formatting input.
    In fact few validators use formatter() any way, and you’re not going to use it at most conditions too.

    A typical validator includes __init__() and __call__() functions, where __init__() is called once validator class instantiated and is used to initialize the object .
    __call__() is called at the end of the execution and acts upon a value
    so validator needs to be called in this way :

    my_validator(value_to_check_against)(value_to_check)
    

    (value_to_check_against is saved as an attribute using the __init__()
    and value_to_check is called by __call__()

    A typical validator should return (value_to_check, None) if validation succeeded and (value_to_check, error_message) if not
    In our case we just made a validator returns (value_after_processing, None) … where None indicates validation succeeded
    We don’t need to have an error message because we use a validator to process data that should be correct .
    How can I guarantee that data is correct ?
    using another validator that is used before my custom one, so that we end up using one validator for data integrity and the other to process data before actually saving into database.

    In our example, we pass function to the validator and in the __call__() we use it to process data and return result.



  • CRYPT() validator

    Not used By default for password field in auth_user table [It should]
    to use it, You need to do somewhere in your model ,something like:

    auth.define_tables() 
    db.auth_user.password.requires=CRYPT()
    

    auth.define_tables() is responsible for creating the default tables each application should have, one of them ofcourse is auth_user and thus :
    db.auth_user.password.requires=CRYPT() should come after it not before it.

    Warning:
    Doing that when you’re already having passwords saved in database means that they won’t work any more unless you made once and only once :

    for row in db().select(db.auth_user.ALL):
       row.update_record(password=CRYPT()(row.password)[0])
    

    Quickly, getting a table of records

    April 28, 2010
  • Of course you know that something like:
    rows = db(db.jobs.id > 0).slect()
    

    yields a Rows object that can be returned using :

    return dict(rows=rows)
    

    and in your view making something like:

    {{=rows}}
    

    will get you a table , yes an HTML table created for you on the fly

  • The problem with this approach is that when you need more customization like decorating your table using java script or doing any other customization you’ll have to create the table manually in the view doing something like:
    <table class="blahblahblah">
    <th> {{T("Title'')}} </th>
    <th> {{T("Location'')}} </th>
    {{for row in rows:}}
    <tr> 
    <td>{{row.title}} </td>
    <td>{{row.location}} </td>
    </tr>
    {{pass}}
    </table>
    

    boring is not it ?

  • We can make another hackish trick which makes our lives easier:
    since Rows object has an attribute called colnames containing the column names of the rows being returned and since column names consists of table_name.field_name:
    you can do something like :

    x = db(db.jobs.id>0).select()
    [column.split('.')[1] for column in x.colnames]
    ['id', 'title']
    

    Now you can do :

    ---- mytable.html ----
    {{def mytable(records, class_name=''):}}
    <table class="{{=class_name}}">
    {{for col in [column.split('.')[1] for column in x.colnames]:}}
    <th> col</th>
    {{pass}}
    {{for r in records:}}
    <tr>{{for k,v in r.items():}}
    <td>{{=v}}</td>
    {{pass}}</tr>
    {{pass}}
    </table>
    {{return}}
    
  • After that all you need to do when ever trying to make a table is to
    import mytable.html in your view with

     {{include 'mytable.html'}}
    

    and use it

    {{mytable(db(...).select(), 'class_name')}}
    

    then you can personalize your table as you want and reuse it.


  • Cool tools for web development

    April 28, 2010

    txt2tags   tinymce  pydns   libgmail  iodbc  win junction [sym links for ntfs on windows]   easy eclipse   Testing tools  yaml  web2py user group search plugin    ulipad   sphinx   firedaemon  edna [mp3 server] flot  sqldesigner and you can check it out here   
    Free layouts   JQueryUI  Breve   send sms  open laszlo  (disqus) An interesting comment system for your site    DotNet Nuke    helpful firefox plugin for developers   Merbivore   Cheetah   How to know visitor’s country  Python captcha extjs 
    JQuery live search 1 and hereopenlayers Change image to icon 
    yslow webx css library Rat Proxy


    helpful tutorials

    April 28, 2010
  • Python fastcgi wsgi and lighthttpd
  • how to integrate openid as your login system
  • In case you want to make an ORM or understand it, you’ve to read much about DBMS :
    you may read about CREATE TABLE dialects:

  • DirectToDiskFileUpload
  • optparse
  • Conditional GET
  • Java script Timeout
  • web2py on webfaction
  • How To Create a User-Defined Service on MS windows

  • REST introduction
  • jsonp
  • access-control-allow-origin-response-header
  • datetime tutorial
  • jquery-tutorial-passing-input-arrays
  • uri-schemes
  • Python eval()
  • Check that
  • Caching
  • python standard library
  • JQuery cheat sheet
  • pubsub concept
  • decorators_rest
  • UsingExtensions
  • MercurialHosting
  • many-to-many
  • Object-relational_mapping
  • Database_abstraction_layer

    <a

  • href=”http://www.agiledata.org/essays/mappingObjects.html”>mappingObjects

  • Setting a form field default value

    April 28, 2010
  • Many times and in certain situations , one needs to set a default (certain) value for a form filed

    suppose you’ve :

  • #in model:
    db.define_table('my_table', Field('my_field', 'string'))
    
    #in controller:
    form = SQLFORM(db.my_table)
    
    if form.accepts(...):
       print form.vars.my_table
    
  • Now I want the ‘my_filed’ to have a default value, may be : ‘Hamdy’
    what should I do ?
  • In fact you should differentiate between 3 suitations:
    • you need the form always to display and accept ‘Hamdy’ as a default value if user didn’t enter his custom text.
      This can be achieved by :

      db.define_table('my_table', Field('my_field', 'string', default='Hamdy'))
      

      or:

      form.vars.my_field.default = 'Hamdy'  # b4 defining the form
      form = SQLFORM(db.my_table)
      
      if form.accepts(...):
         print form.vars.my_table
      
    • The second situation is that the default string is variable depending on some conditions in this case, one should always use :
    • form.vars.my_field.default = 'Hamdy'  # b4 defining the form
      form = SQLFORM(db.my_table)
      

      which is suitable for almost all conditions

    • The 3rd situation is when you have a classic form, may be using :
      form = FORM()
      

      you can use Field(”), default=….) in it but what if the default value is variable ?
      you can’t set the value using db. …… since the form is not dealing with a database table so what can you do ?

      In this case make something like :

      form = FORM()
      form.vars.field = 'Hamdy'  # after the definition of the form
      if form.accepts(..., ...):
        # do something
      

      This technique is also very useful for SQLFORM that is dealing with a database table but in a certain situation you added to it an additional field (field added to form not to db table).
      In this case you can still play with it using this method.

  • To this extent, I guess you’re almost get how to deal efficiently with web2py forms, but I still have more 🙂
    One another interesting problem arises when you set in your model a field to be readable=False, writable=False and this’s a common situation when using a timestamp (creation_time) field in youer database table, in such a case you do something like :

    db.define_table('my_table', Field(...), Field('timestamp', 'datetime', readable=False, writable=False, default=request.now))
    
  • Now when ever trying to make a SQLFORM out of this table, user will not see the timestamp field , it will be updated though when submitting data.
    In fact readable=False, writable=False prevents this field to be a prt of the form.
    So having in my model :

    db.define_table('toto', Field('lolo'), Field('soso', readable=False, writable=False, default='hamdy'))
    

    and in my controller :

    def index():
    
        form = SQLFORM(db.toto)
        if form.accepts(request.vars, session):
            print form.vars
            form.vars.lolo = 'yet another value'   # -> not working
            response.flash = T('form accepted')
        return dict(form=form)
    
  • user will see one field ‘lolo’ and when trying to print the form.vars upon accepting it, you’ll find no existence for the ‘soso’ field
  • trying to set this a value for this field upon accepting the form using

    form.vars.lolo = 'yet another value' will not work also
    

    database will have the default value which is ‘Hamdy’ for this field for every new record you try to create.

  • what is going to work is to set the default value before defining the form at the database level not on the form level , Since form doesn’t really include this particular field :
      db.toto.soso.default = 'Another value'   #working
      form = SQLFORM(db.toto)
    
  • At this level there’s still no problem, the problem in fact will appear whenever you try to make additional check on this particular field value
    upon accepting the form.
    Say for example you made :

      db.toto.soso.default = session.name  #working
      form = SQLFORM(db.toto)
    
  • Now suppose you want to make additional check for this session.name variable to make sure it’s not just a garbage.
    In such situations you may use the onvalidation function while accepting the SQLFORM form so that more validation can be done

    def check(form):
        if form.vars.soso == 'Not hamdy':
            print 'Not hamdy'
            form.vars.soso = 'Not Not Not hamdy'
    
    def index():
        db.toto.soso.default = 'Not hamdy'   #working
        form = SQLFORM(db.toto)
        if form.accepts(request.vars, session, onvalidation=check):
            response.flash = T('form accepted')
        return dict(form=form)
    
  • Now as you see check() function is evaluated but does nothing since there’s no existence for a form.vars.soso since the field itself is not a part of the form

    SO what to do?

    It’s simple , in the definition of SQLFORM you can choose what fields you want in the form
    so you simply do something like:

    def check(form):
        if form.vars.soso == 'Not hamdy':
            form.errors['lolo'] = "There's an error"
                    
    def index():
        db.toto.soso.default = 'Not hamdy'   #working
        form = SQLFORM(db.toto)
        form.vars.soso = 'Not hamdy'  # it's a python magic
        if form.accepts(request.vars, session, onvalidation=check):
            response.flash = T('form accepted')
        return dict(form=form)
    
    

    form.vars.soso = ‘Not hamdy’ is just a python magic, being able to create and set an object attribute on the fly and it really just a variable
    not related to the form .
    we just created it to check the value.

  • The last problem that may face a user is that he/she may have to display this field in some certain situations but in others it should be hidden.
    Now it’s time for a user to decide what is the default case should it be hidden or shown by default.
    If it’s hidden by default you can show it in SQLFORM by using

     form = SQLFORM(db.toto, fields=['lolo', 'soso'])
    

    By using fields=[] you can choose what fields to display

    and if the the other case is the default, you can hide the field using

    db.soso.readable = False
    db.soso.writable = False
    form = SQLFORM(db.toto)
    

  • Upload Download files

    April 28, 2010
  • Using multiple tables in the same page as you know requires explicitly adding form name when you accept it
  • suppose a situation in which you need to make multiple upload forms in the same page may be for users to upload their cvs
  • Now you’ve 3 problems :
    • How could you add multiple forms in the same page and in the same time make them work ?
    • How to upload the files (cvs)
    • How to download them
    
    def jobs():
            ...............................................
            ...............................................
            jobs = db(...).select(...)
            for job in jobs:
                # I'll use the same name for form name as well as the field
                formname = "upload_f_%s"%job.id
                form = FORM(INPUT(_type="file",_name=formname,
                              requires=[IS_NOT_EMPTY(),
                                        IS_LENGTH(1048576, 1024, error_message=CustomMessages.UPLOAD_CV_SIZE)
                                       ]
                              ),
                        INPUT(_type='submit'))
            
                if form.accepts(request.vars, formname=formname):
                    stream=eval('form.vars.%s.file'%formname)
                    filename= eval('form.vars.%s.filename'%formname)        
                    file_id = db.cvs.insert(cv=db.cvs.cv.store(stream,filename=filename),
                                        job_title=job.title,
                                        job_id=job.id)
                
                    # add permissions for that file    
    
                    # do other stuff       
    
  • As you see , I made a form with a field of type ‘file’ and form name is variable based on the job_id , C.Vs are going to be uploaded
    this helps making multiple forms per page and in the same time every form has a unique name that will be used when accepting the form .
  • Now as you may have guessed the form containing a ‘file’ field will have (when being accepted) :
    form.vars.field_name.file  -> get the reference to the file
    form.vars.field_name.filename  -> get the file name
    

    Now you can easily do something like:

    stream=form.vars.field_name.file
    filename= form.vars.field_name.filename
    

    Now you can store your file name into the database

    db.cvs.insert(cv=db.cvs.cv.store(stream,filename=filename),
                                        job_title=job.title,
                                        job_id=job.id)
    
    

    see the :

    db.table_name.field_of_type_upload.store()
    
  • Congratulations !!! you’ve uploaded your files

  • Now for downloading files you can do :
    def download_cv():
        file_id = request.args(0)
        import cStringIO 
        import contenttype as c
        s=cStringIO.StringIO() 
        
        (filename,file) = db.cvs.cv.retrieve(db.cvs[file_id].cv)
        s.write(file.read())  
        response.headers['Content-Type'] = c.contenttype(filename)
        response.headers['Content-Disposition'] = \
                    "attachment; filename=%s" % filename  
        return s.getvalue()
    
    

    Now you can make another function that list all cvs available with a link for downloading them as follows:

    def list_Cvs():
        cvs = db(db.cvs.id>0).select(db.cvs.cv) # db.cvs.cv is of type 'upload'
        urls = [A('Download', _href=URL(r=request,\
                                                   c='files',
                                                   f='download_cv', args=[row.id]
                     )) for row in cvs]
        return urls
    
  • what is the benefit of writing my own download function ?
    This enables you to write your own authorization logic before allowing a user to download a file

  • Now what if I just don’t want to write my own download function and use web2py facilities for that matter ?

  • You can use response.stream(), or response.download() functions.
  • What is difference between them?

  • In fact response.stream is the main download function that takes care of streaming files.
    response.download() calls response.stream() to do the streaming stuff.
  • response.download() has its arguments as request, db and is used for downloading files by their names, while the name is the name of the file in the database.
                def download():
                    return response.download(request, db)
            #downloads from http://..../download/filename
    

    response.download() takes request to extract from it the file name stored in [request.args]

    download function is mainly used by SQLFORM to update a record that includes an upload field that is used to upload an image, in this case response.download() gets the file (image) to be displayed when updating this record.

    form = SQLFORM(db.my_table, record, upload=URL(r=request, c='default', f='download'))
    
  • Suppose you want to stream an MP3 file, you can do something like:

    Somebody asked how to stream an mp3 file from the uploads files directly:
    def get_my_file():
          filename=request.args[0]
          path=os.path.join(request.folder,'uploads',filename)
          response.headers['ContentType'] ="application/octet-stream";
          response.headers['Content-Disposition']="attachment; filename="  
    +filename
          return response.stream(open(filename),chunk_size=4096)
    

    web2py zen

    April 27, 2010
  • Web2py is a WSGI compliant enterprise web framework .
  • Enterprise” here means mainly one thing: we DO NOT CHANGE THE API because professional users who works in teams and on long term projects must count on stable API add documentation. “Enterprise” do not mean we focus on very large enterprises, we probably focus more on small and medium size ones, nor it means we have every possible “enterprise” feature. We are very straightforward about the web2py features. “enterprise” here sends a message: web2py is not developed by a bunch of kids who try to follow the latest trends and never deliver a stable product. web2py is built by experienced developers who know how to find a balance between usability, stability and features.
  • WSGI server parameters can be passed as command line options
  • Always promises backward compatibility
  • Web2py is not planned to move to python 3 any time soon because
    it will break backward compatibility of all applications and because
    database drivers do not work on 3. Moreover web2py apps would no
    longer work on GAE.
    The main and probably the only issue is with strings becoming unicode
    strings by default. It would not be difficult to change web2py to
    work with 3.0 and it was designed following all the other 3.0
    guidelines but there is no way to make the apps backward compatible.
  • you can make your web2py interact with your cgi scripts :
    You can run web2py on a port (say 8000) and your CGI script on a
    different port (say 8001) using a different web server.
    In this case the web2py program can call the CGI scripts pass parameters and receive response. Example

    import urllib
    data=urllib.urlopen('http://localhost:8001/myscript.cgi?
    parameter=value')
    

    You can read more in the urllib and urllib2 documentation).
    You cannot call the cgi scripts from web2py without going over HTTP.
    This is not a web2py limitation, this is a CGI one. In fact CGI
    assumes that every CGI script is executed in its own process and thus
    has its own folder, environment variables and stdout/stdin. Therefore
    a CGI script is not thread safe and cannot be executed inside a
    thread (threads shares folder, environment and IO streams). web2py
    uses threads.

  • web2py does support IF_MODIFIED_SINCE and PARTIAL REQUESTS out of the box.
    You can add any header you want including ETAGS.
  • There’s a routing system in web2py which unfortunately doesn’t work on application level basis (yet)
    Warning:
    Don’t use the routes module to enforce the use of SSL on a few URLs
    it would not be safe. If you are behind a proxy web2py does
    not know whether the original request was over https or not. The
    method of using X_FORWARDED_FOR has known vulnerabilities. You should use apache to force SSL.
  • Web2py runs on :
    • runs on python >= 2.4 but two things to note:
      • if you save data using CRYPT() validator used with password fields in 2.4 you will not able to read them in 2.5 or 2.6 so be careful python 2.y doesn’t have hashlib used by CRYPT() validator
      • There is not uuid module in Python2.4 , You could make one that will satisfy web2py. You can make it as a module ofcourse
        ## uuid.py 
        import random,time 
        def uuid4(): return '%s%s" % 
        (int(time.time()),random.randint(100000,999999)) 
        ## end file 
        
    • web2py runs on jython.
    • No support for stackless python [yet] and using it actually causes errors
  • Web2py philosophy is not to use separate and un-integrated modules.In fact for some of the web2py components there is a better module out there, the point is that the web2py modules are designed to work together while the alternatives are not.
    You will not appreciate this until you try it. Here is an example: Pygments is a much better general purpose syntax highlighter than the web2py’s one, nevertheless web2py’s one can highlight web2py code, create clickable links from web2py keywords to the web2py online documentation, is faster and fits in 10k. If you need to syntax highlight Java or PHP code you can still easy_install and use Pygments. Although you can, the web2py modules are not designed to be taken out and used separately.
  • Web2py’s philosophy is : if you want scalability, it is best to store as much as possible on disk and use a centralized database when you need transactions and joins.
    This is why web2py by default stores sessions and files on disk.
  • Web2py vs others
  • From Django to web2py
  • From TurboGears to web2py
  • From Rails to web2py
  • Web2py for J2EE programmers
  • from php to web2py
  • web2py can run on a cluster environment like OpenVMS.In fact This is not a problem on web2py as long as all processes see the same
    filesystem. If they do not see the same filesystem you will not be able to use sessions, tickets and upload files (unless you do some
    tweaking)
    Check this section in the manual book
  • web2py suits agile development, with an interactive shell used for testing, debugging and experimenting with your applications.
    you can run interactive shell that will run in ‘ipython’ 😀 by doing something like:

    cd web2py
    python web2py.py -S application_name -M
    # -M means to import also all the models in the application
    

    and congratulations, you can do something like:

    print db.tables
    

    to get list of all database tables used by this application.
    You can ofcourse do more .
    In fact one of the interesting stuff that you can make is:

    python web2py.py -S application_name -M -R file.py
    

    the interesting thing is that file.py can include code that will be executed as if it were a part of a controller.
    If the application specified by -S doesn’t exist, shell offers you to create it. isn’t that cool? 😀
    you can also import your custom modules and use it inside shell:

    exec('from applications.%s.modules.my_custom_mod import *' %(request.application))
    

    Your module will run in its own context, so if you want to do some operations like manipulating request, or some database stuff, you have to pass those objects to your module functions or class explicitly when calling them, this implies of course that you define your functions or classes with that in mind

    class DoThat(object):
        def __init__(self, request, db, cache, T):
             .....
        ......
    

    To execute a model file of another application:
    [soucecode]
    execfile(os.path.join(request.folder,’../other/app/models/db.py’))
    [/sourcecode]

    You can use the previous mechanism to execute other application controllers but there may be issues in importing controllers in other ways since they may contain authorization code outside functions. and it’s not a good idea to import controllers .

    you can even run the shell without ipython if you just don’t want it
    simply pass the -P (uppercase) argument when trying to run the shell.
    Warning:
    In the shell you have to explicitly db.commit() or db.rollback() your transactions.

  • Web2py actions support doctesting, but becareful …. doctets are not thread safe. This is not because of web2py. All
    testing libraries in python are not thread safe because they redirect
    sys.stdout.
  • In fact The web based administrative interface can only test
    doctests in controllers. The shell has a -test option that will run
    any test you like and this does not require web2py running.
  • Web2py admin interface doesn’t allow remote access unless it is secure, other wise connection is denied.
    You can access it locally though without these restrictions, only admin password is required.
    Admin should be used for development and should never be exposed.
    If you want to expose admin:

    • make sure it goes over HTTPS
    • always logout when done
    • Edit admin/controllers/default.py and at the top write:
      response.cookies[response.session_id_name].secure=True
      

      The secure cookies are not enabled by default because admins usually access the admin application through their lcalhost, but it you’re tending to access it remotely you should add secure cookies.

    • Moreover all the */appadmin/* pages should go over https.
    • Another way , that may or may not be easier , is running two
      instances of web2py on different ports. One is exposes by without a
      password and so no admin. One is not exposed, runs only on localhost
      and has a password for admin. Then you connect to the second via a
      ssh tunnel. This is very secure, easy to setup, and you can do
      everything you do now.

    If somebody intercept your communications and steals the session
    cookies for admin, they can become admin.
    These rules apply to web2py as well as to every system that does
    authentication. even gmail has this problem.
    To make things even more secure admin session is default to expire after 10 minutes.

  • Web2py forms including SQLFORM, SQLFORM.factory, all inherit from class FORM and you access their components via form.components:
    ex:

    form.components[0].components[0].components[1]
    

    or you can deal with forms as list of lists and edit its components according to your needs [just print a form and youi’ll know how to access it using this method.

    form[0][..][..]
    

    Warning:

    It is never a good idea to access form components since the internal
    implementation may change in the future (Although there ‘re no plans to do so).
    you can access them that way if there’s no other way to do so.

  • Web2py allows you to byte code compile applications and distribute them .
    you can even distribute your applications in a compiled binary files.
    This way, one of the advantages is that templates are only parsed
    once when the application is compiled and this makes web2py apps fast
    Warning:
    If you are using the binary distribution of web2py. It ignores
    your python installation because it uses its own.
    This may cause some errors when trying to import some modules.
  • Web2py is an MVC frame work , while all models are executed for every request.
    Technically a model file is not a module because they access symbols
    that are only defined in the context they are intended to be executed
    (file request and response). So importing a model explicitly can
    create problems.
    Put stuff in models if:

      Have something to do with accessing db data or helpers for visualizing db data
      They consist of a one single file with no dependences
      The code only makes sense inside a web2py app and I would not be reusing it outside web2py

    To create your tables, you may either do it manually or use a web based tool for this purpose.
    It’s able to generate web2py’s DAL compatible code.
    This great tool can’t be a part of web2py framework itself because its license conflicts with web2py’s license that have an exception to ship the binary web2py code with your web applications without the source code as long as you didn’t touch the source code .
    You can’t use controller functions in another controller because technically controller is not a module.
    you need to gather all your common functions,and put them inside a model or module, or even in gluon.contrib so that they can be accessible to all your applications without no problem

    When a request comes to a controller the requested controller file is loaded this is not achieved using reload() but exec() which executes the controller file and only takes about 0.03 seconds only.
    Using exec() also has the advantage that the framework does not
    need to monitor modules for changes before reloading (like Pylons)
    which may cause a slow down for apps with multiple files. web2py only
    execs those controllers that are requested.

    For framework like django, application is just the reuse unit, but not the execution unit. And in web2py app is execution unit, but
    not reuse unit. For example, I have user management app, and I want to reuse it, in Django, I can import the user model, user controller
    functions, and use template also. But in web2py I can’t directly
    import and reuse them. Only I can think out is copy the file which I
    want to use to target app. There are many ways to combine different apps together, but the usage of exec make it difficult. And how to orginaze the development unit and execution unit is a design issue. If we only care about the execution unit, so how to use others app functionalities in our app? Only through xml-rpc? Or copy the files into the application.

    In the contrary:

    There are also other problems with modules related to the search path
    and different applications may end up with conflicting modules.
    There may also be conflicting classes because all modules would be
    imported in the same context and if two modules have classes with the
    same name they would overwrite each other. This is not an issue if one just made an import like:

    from app1 import Class1
    from app2 import Class1
    

    Now you can use app1.Class1 or app2.Class1 wihtout any problems.

    In web2py exec() behavior is similar to:
    For example:

    a=""" 
    class A: 
        name='a' 
    print A.name 
    """ 
    b=""" 
    class A: 
        name='b' 
    print A.name 
    """ 
    c={} 
    exec(a,{},c) 
    exec(b,{},{}) 
    exec('print A.name',{},c) 
    prints 
    a 
    b 
    a 
    

    which is nice: the two classes called A ignore each other. If you use
    modules you end up with a lot of potential conflicts between multiple
    apps. In Django for example you would have to careful in designing
    apps that do not conflict. In web2py you do not need to think about
    it. You have to do a little of extra work to share stuff but at least
    you know for sure that no unwanted sharing takes place.

    the ‘exec’ have a good thing , that is the module can be GC by python afte request is over.

    sometimes you need to call some controllers functions and pass to them some variables[request variables] to make some functionality based on the values of these variables.In this case you may face one or more situations like those:

    • If you are doing a redirect to a controller function that is
      supposed to receive user input, you use :

      URL(r=request, c='controller_name', args=[...], vars=dict(..=.., ..=..))
      

      args are list why ? It allows you to do ‘/’.join(request.args) and rebuild the original string easily.

      vars is a dictionary why ? because this is the best fit for it key/value pairs .

    • If you want to call a controller function that is not intended to
      receive user input and is in the same controller, save the variables
      in session and retrieve them later.
    • If you want to call a controller function that exposes some
      functionality but has no state (so no use of sessions), expose it via
      xmlrpc .
      You can use urllib2.urlopen to call other functions, so you can do something similar to the following
    • example:
      Warning: This’s just an example made for test purposes to clarify things.
      Assume application name is ‘t2’

      def index():
          return dict(url=A('click here', _href=URL(r=request, f='another', args=['a'], vars=dict(b='b'))))
      
      def another():
          print response._caller(another)
          import urllib2, urllib
          if request.args(0) and request.vars.has_key('b'):        
              test_values = {'hidden_var' : 1}
              data = urllib.urlencode(test_values)        
              try:
                   req = urllib2.urlopen('http://127.0.0.1/t2/default/third?%s'%data).read()             
                   return dict(x=XML(req))        
              except Exception, e:
                   print 'Error:', e
      def third():
          form = SQLFORM(db.my_table, request.vars.hidden_var)
          if form.accepts(request.vars, session):
              pass
          return form
      
  • Web2py includes a separate folder for your custom modules that you want to use, in this way you can use your own python libraries in your web application.
    things to note when using modules:
    Put stuff in modules if:

      The do not require access to request, response, cache, session and thus can be used with ot without web2py .
      They consist of multiple files
      I need them only in some (but not all) controller functions.
  • whenever you want to import something from a module don’t do something like:

    • from applications.yourapp.modules.Custom_Validators import IS_AAA
      

      making your import dependent on the name of the app is not a good idea, instead use something like:

      exec('from applications.%s.modules.validators import IS_AAA' %  
      request.application)
      
  • modules can’t see session, request, response objects of web2py, if you want to make operations using one or more web2py objects, you’ve to make a module function that takes those objects as its parameters.
  • The first time you need to run web2py with all its files. After that
    you can remove any installed application you want including admin,
    examples and welcome.

    Nothing breaks except that you can no longer visit pages that you do
    not have. You only get an internal error if you try to do that.

    welcome.tar is the scaffold application. That’s the one file you
    should not remove.

    Notice that if you remove admin you can no longer login as
    administrator and the database administration (appadmin) will be
    disabled for all you apps, unless you adit the appadmin.py files and
    change the authentication mechanism.
    You may need to rename your applicationa ‘init’, so that it can be the default application (the one that starts, once you start web2py) .

  • In web2py (and many web frameworks) each request is served by a different thread. This if done for speed. The different threads share
    the same memory space and the same environment variables. By default, you cannot execute in a thread any function or module that attempts to change environment variables or gain exclusive access to memory or other OS resource without mutex locking.
    For example you cannot do os.chdir(‘somedir’) else all threads would
    change folder and web2py would behave weird.
    There are ways many around this. Run processes, not thread; perform a
    mutex lock; create a background process that access exclusively the
    thread-unsafe module.
    So be careful :
    When ever making a web application using web2py, DON’T CHANGE THE CURRENT WORKING DIRECTORY , DON’T USE os.chdir() in your web applications.
    Changing working directory may cause your application to fail and moreover it’s not thread safe.
    To know more about this issue and more, check this interesting topic in the web2py user group:
    Very, Very interesting discussion

  • web2py can serve xmlrpc requests (even to itself, without deadlocks).
  • when uploading files using web2py, they’re renamed by adding to the name a random string .
    This is important for situations like :
    If the real name conflicts with another file or
    contains characters not supported by the file system
  • Web2py provides an easy way to access cookies:
    The value can be a string or a Morsel Object .
    Check that for more info
    Do Not Use cookies your self, and store everything always server side.
    Let web2py manage session cookies for you, it’s done automatically and you need not to worry about any thing.
  • web2py provides a good mechanism for internationalization through the T object that supports the lazy translation mode and immediate mode
    More information about T
    T returns an object that can be serialized as a string
    web2py does not allow you to do :

    T("bla")+T("bla")
    

    but it does allow :

    T("bla %(name)s",dict(name='Tim')) 
    

    why?

    • You need to be careful concatenating strings. String concatenation is one of those “no-no”s of internationalization.
      The reason for this is that different languages have different sentence
      structures.For instance, some languages negation is before a word and other’s negationis in other parts of the word.Many slavic languages, like Czech, have the interesting feature that word order isn’t particularly important, so for Pete’s sake don’t start with one of those as your base language that everything’s translated too.The worst example is something like German where a negation can happen in two different parts of the sentence, and you just get screwed concatenating that string.If you’re gluing together strings, or you need to put dynamic content in an internationalized string, it’s really best if you put it in a string that’s parameterized: “hello %(name)s”, dict(“name”: “Tim”)
  • Web2py makes a good use of decorators to make your life easier
    for example:

    @auth.requires_login()
    @auth.requires_memebrship('admin')
    def do_it():
        # This won't be executed unless user is logged in and belongs to the 'admin' group
    

    Web2py philosophy is not to use decorators for validation since decorators are associated to a function (i.e. a page) while validation is associated to a form (and a page can have multiple forms).
    A form should be an object that knows how to validate itself.

  • Web2py mixes between the database tables and forms that should enter data into those tables; by using SQLFORM you can deal with a database table and enter data into it directly.
    ex:

    #in a model:
    db.define_table('my_table', Field('my_field', 'string' ,requires=[....]))
    #in a controller
    form = SQLFORM(db.my_Table)
    .........................................
    
    • “requires” is assigned one or more validators [they work on form level not database level], i.e IS_NOT_EMPTY()
      To make a mix between validators you just add them to the list assigned to “requires”
    • A validator is a two way filter.
      user_input -> validator -> data_for_db OR error
      user_output <- validator <- data_from_db
      
    • using multiple validators at the same time makes sense and it’s just as if they’re ANDed together.
    • AND makes sense because it is like piping validators. When data
      goes in it goes through one validator after another and has to pass
      them all. If it misses one that one returns the error message. When
      data comes out it goes through the same validators in reversed order.
    • OR is problematic because if user input does not pass any validator,
      which error should be generated? The error is different that the
      errors associated to the individual validators.
      Moreoever when data comes out which validator should do the
      formatting? Consider this example:

      IS_DATE('%Y-%m-%d') OR IS_DATE('%d-%m%Y')
      

      This cannot be.
      To understand this well, consider this example:
      consider IS_DATE
      it has a constructor a __call__() method and a formatter method,
      when data is validated in a form it is filtered by IS_DATE.__call__
      and a string, say ’01/01/2007′ is converted to a datetime object.
      when data is presented into an edit SQLFORM or a SQLTABLE, formatter , it is called and the datetime object is converted back to ’01/01/2007′.
      The constructor takes an argument that specifies how the formatter
      can be done.
      If you have a list of validators and they all pass the the __call__
      method, they are called in the order of the list and the formatter methods are called in reversed order.
      Not so many validators use formatter method, but the problem is that : wil this continue for ever ?
      People can write validators that take formatter method and thus using OR will be problematic.

    • The bottom line is that in order to implement an OR
      some combination should be allowed and others should be forbidden. This will make individual validators more complex objects that they are now and their behavior less intuitive.
    • The only Validator to use OR is : IS_EMPTY_OR()
      ex:

      IS_EMPTY_OR(IS_URL())
      
  • To build a great and rapid development environment, dictionaries returned by web2py’s actions [controller functions] are automatically rendered by a generic view , without the need to make a view file for this action .
    This’s done as you may know using a generic view files that use the
    response._vars which holds the returning values of the action [function]
    and is rendered using

    {{=BEAUTIFY(response._Vars)}}
    
  • Web2py can supports both POST and GET variables together sent with each other and you can extract each set.

     request.post_vars, request.get_vars
    

    Web2py takes care of the situations like when MS-Windows user input data which will be sent with ‘\r’ in the end of your input [‘\n\r’ is the line terminator in windows but not in linux .. In linux it’s just ‘\n’] .any way user input will have to be filtered using something like:

    string.replace('\r', '')
    
  • One another greatest thing is that you may not create a view file for every action you want to expose:
    • you may edit the generic view file [generic.html] which includes the following lines of code :

      {{extend 'layout.html'}}
      {{"""
      
      You should not modify this file. 
      It is used as default when a view is not provided for your controllers
      
      """}}
      
      {{=BEAUTIFY(response._vars)}}
      
      <button onclick="document.location='{{=URL("admin","default","design",
      args=request.application)}}'">admin</button>
      <button onclick="jQuery('#request').slideToggle()">request</button>
      <div class="hidden" id="request"><h2>request</h2>{{=BEAUTIFY(request)}}</div>
      <button onclick="jQuery('#session').slideToggle()">session</button>
      <div class="hidden" id="session"><h2>session</h2>{{=BEAUTIFY(session)}}</div>
      <button onclick="jQuery('#response').slideToggle()">response</button>
      <div class="hidden" id="response"><h2>response</h2>{{=BEAUTIFY(response)}}</div>
      <script>jQuery('.hidden').hide();</script>
      
      

      this stuff is useful in development time since it gives you buttons to check session variables, request and response but in production you may just make it look like:

      {{extend 'layout.html'}}
      {{=BEAUTIFY(response._vars.values())}}
      

      and bingoo !!!!!! you get every thing almost automated and you don’t need to add one view file per action .
      Ofcourse this is not practical all the time , and in real-life you always have some thing to add to the view but sometimes you don’t have 🙂
      and you can rely on the generic.html then to render your view.

    • Another situation is that you can make use of one view file in different actions in different controllers … wooooow !!!!
      look at this example :

      def test():
           response.flash=T('Welcome to web2py')
           response.view='default/view.html'  ### this indicates the view file
           return dict(message=T('Hello World'))
      
      #Here's the same version of the function but more suitable for caching the view .
      
      @cache(request.env.path_info, time_expire=5, cache_model=cache.ram)
        def test():
           response.flash=T('Welcome to web2py')
           response.view='default/view.html'
           return response.render(dict(message=T('Hello World')))
      
      
    • Web2py views are different than django’s and Macko templates, in web2py : If a variable is accessed in the view, if has to be defined.
      in django, it just ignore it
      so in your view in web2py, if you’re returning a form that may sometimes have no value, you’ve to make additional check in the view:

      {{if reponse._vars.has_key('form'):}}
      # or
      {{if form:}}
      
    • One another interesting feature that suits the rapid development environment is that you can have multiple views per action(controller function), that is it , you can render output as html, rss, xml.
      You can do this by either depending on the generic views files “generic.xml, generic.xxx, …” that will render different actions based on the extension you provide in the url or you can make your own views, ending with different views for one action like [index.html, index.xml, ….]
      You can just open up one generic view file and follow the same behavior in your custom view files for other extensions other than html

      def index():
         form = FORM(INPUT(_name='Name'), INPUT(_type='submit'))
         if form.accepts(request.vars, session):
            pass
         return dict(form=form)
      

      Now trying to access page as index.html will return the form as expected, but trying to access index.xml will return something like:

      <document>
      −
      <form>
      <form action="" enctype="multipart/form-data" method="post"><input name="Name" type="text" /><input type="submit" /><div class="hidden"><input name="_formkey" type="hidden" value="43ab2943-2f1c-4ae6-bdaf-73e3224967ee" /><input name="_formname" type="hidden" value="default" /></div></form>
      </form>
      </document>
      

      Can you see the beauty of this? You can use similar behaviors for debugging without trying to print the form itself in your code.
      Faster right ? easier right ? 😀

  • No daemons [except for cron]
  • Daemons tend to need starting/stopping and affect application portability.
  • If you’ve long running processes run by a thread , server would kill it any way. you need your daemon to run it
  • It is not a good idea to store the entire file in the db. better to store name only. That’s why web2py saves uploaded images to the directory called ‘uploads’ and the name in the db.
    In fact looking into gluon.sql.py, you’ll find something like:

    if fieldtype=='blob': 
             obj=base64.b64encode(str(obj)) 
    

    web2py is not currently using blobs by the book. The reason is that
    blob values need to be escaped differently by different database
    backends and in some cases this is not well documented. web2py avoids
    the problem by storing the base64 encoded data, thus using the blob
    as a text field.
    The current behavior has both advantages (simpler code, faster encoding, humanly readable SQL string all the time, works with databases that may not have a blob type) and disadvantages (the storage is increased by 30%, you cannot search with LIKE,, in a blob).

  • Field('blobf','blob')  # Not Recommended
    Field('uploadf','upload') # Reommended
    
  • There’re 3 reasons for using error tickets for displaying errors:
    • Not to separate between production and debugging modes.
    • It is conceptually possible to cause bad errors that Web2py
      may not be able to read the file that contains the error and even
      requires web2py restart.
    • No configuration files for the framework itself, but you can make your own configuration file for your web application.
  • Error messages are by default saved on file system not in database why?
    Simply because in development time most errors come from database itself, and thus errors won’t come if they’re stored there.
    And because web2py’s philosophy is than no separation between development and production stages, it’s the best choice to have errors stored on file system.
  • No more template languages, only python code.
    This doesn’t mean that you can’t use other template languages.
    You can use easily use your favorite template language.
    Django’s philosophy is to let view to designer and use template languages because in most cases designers are not programmers, but this’s not web2py’s philosophy.
    In fact, using web2py you can return to the view all elements that you want and just let designer control how things look like and when a designer needs to do some customization, he can still use usual HTML tags.

    • In your view you can use {{}} to write your python code into it
    • Multi lines are allowed between single {{}}.
    • no indentation is required, when using python in views
    • if statements, for, and while need to be closed using {{pass}} because in view , there’s no indentation
    • {{if x > 6:}}
      {{do_some_thing}}
      {{else:}}
      {{pass}}
      
    • web2py can have any implementation of any template language, its design allows so but why would one trade python for a template language ? !!!
  • unpickeled objects stored in session causes problems.ex: trying to store in session a database table object causes aplication to crash
  • session.table = db.my_table   # Don't do this
    

    SQLDB objects are not pickleble because of the open connection.
    In fact you cannot store objects that belong to a class starting with SQL*, i.e. connections, record sets, queries, individual records, etc. You also cannot store classes (only objects), functions and lambdas.
    [classes starting with SQL like SQLFIELD are having short names now like Field, ….. both names are working in fact ]

    user = db(db.users.username==username).select().first()
    You cannot store a user object in the session.The reason is that user has a method user.update_record which requires a db connection and it is not serializable.

    If cPickle.dumps(obj) does not raise an exception than you can do
    session.obj=obj

  • web2py provides an ajax app that provides a python console.
    It uses pickle to store state therefore it is somewhat limited in what it can do and it has security issues but it is a fun toy to play with and show off python.
    Too bad in its present for it cannot be used to interact with SQLDB
    which is not pickleble because of the open connection.
  • It is standard in MVC frameworks including web2py that each page/form is a self submitting and it is uniquely associated to a controller function (Rails calls them actions). The reason is that a form knows how to validate its own input variables. Upon validation the page redirects to a different page(action). In web2py URL builds URLs within web2py.
    So generally it’s a bad behavior to have a form to validate inputs of another form

    For more Information click here

  • web2py prevents double submission of forms using a unique key passed to the form accepts() function via session.
    It makes sure if you click on a form twice, it is processed only once. This prevents user error and some forms of reply attacks. If you do not pass the session variable this mechanism is disabled.

    if form.accepts(request.vars, session)
    

    This mechanism fail though if you’ve multiple forms in the same page
    and in this case we should pass to the accepts function of every form explicit and different form names to distinguish between forms when they’re being accepted.

    if form1.accepts(request.vars, formname='custom_name'):
        #do_something
    if form2.accepts(request.vars, formname='custom_name2'):
        #do_another thing
    
  • Web2py had its own Database Abstraction Layer, the thing that bothers some people and push them to argue about the benefits of this.
    and why not using say for example SQLAlchemy the famous ORM.
    SQLAlchemy is better than the web2py ORM in dealing with legacy databases. web2py has restrictions in this case. But the web2py ORM is much better integrated with the rest of the framework than SQLAlchemy is integrated with, for example, Pylons or TurboGears. If you do not use the entire web2py framework you are better off with SQLAlchemy. If you do use web2py, you are better off with its own ORM.

    Any way the new Google appengine Bigtable datastore makes any SQL-based ORMs moot now anyway, so all we really need to worry about are the business logic and presentation, both of which web2py excels at.

  • web2py’s Database Abstraction Layer (DAL) supports many kinds of RDBMS like sqlite, mysql, oracle, …..
    In fact any new application created by web2py has a support of sqlite by default and this’s on purpose because this provides a quick solution for making an application that’s up and running on the fly without many configurations required or something.

    To change this [may be in a real production mode], you’ve to change one line in models/db.py from

    db = DAL('sqlite://storage.sqlite')
    

    into the appropriate dbms url in your system, for example to support mysql you simply have to do :

    'mysql://username:password@localhost/test'
    
  • More interestingly, you can use DAL without database using :

    db = DAL(None)
    

    then you can define tables, and create SQLFORMs from those tables and test the validation mechanism
    and generate the real sql queries generated by DAL and that are hidden by the DAL syntax

    # Model
     db = DAL(None)
    db.define_table('members', Field('name', requires=IS_NOT_EMPTY()))
    
    #Controller
    def index():
        form = SQLFORM(db.members)
        if form.accepts(request.vars, session):
            response.flash = T('hey it worked')
        rows=db().select(db.members.ALL)
        print db._lastsql
       return dict(form=form)
    

    Congratulations !!! without need to introduce extra/new syntax.
    Internally DAL(None) behaves like a sqlite db and you can use it test query generations as well but there is no sqlite file so nothing is stored and no overhead.

  • Things to take care of when using sqlite though are :

    • SQLite locks the database. Only one thread can safely access it.
    • Only the RENAME TABLE and ADD COLUMN variants of the ALTER TABLE command are supported. Other kinds of ALTER TABLE operations such as DROP COLUMN, ALTER COLUMN, ADD CONSTRAINT, and so forth are omitted.

      If you want to make more complex changes in the structure of a table, you will have to recreate the table. You can save existing data to a temporary table, drop the old table, create the new table, then copy the data back in from the temporary table.

      For example, suppose you have a table named “t1” with columns names “a”, “b”, and “c” and that you want to delete column “c” from this table. The following steps illustrate how this could be done:

          BEGIN TRANSACTION;
          CREATE TEMPORARY TABLE t1_backup(a,b);
          INSERT INTO t1_backup SELECT a,b FROM t1;
          DROP TABLE t1;
          CREATE TABLE t1(a,b);
          INSERT INTO t1 SELECT a,b FROM t1_backup;
          DROP TABLE t1_backup;
          COMMIT;
      
    • To learn more about sqlite you can take a look at :
      Features not supported by sqlite
      Sqlite faq

  • Previous limitations belong to Sqlite only, other dbms runs smoothly
    In fact to ensure that web2py is helpful in an agile environment,
    web2py’s Database Abstraction Layer (DAL) supports migration,
    so you can easily make something like:

    db.define_table('my_table', Field('my_field', .....), migrate=True)
    # migrate=True
    

    setting migrate to True comes in rescue in the development time, you can just change the structure of your table [add more fields, remove ones] and your changes will take effect on the fly, upon the next request [all models are executed at every request and thus those changes will take effect then if migrate = True].
    This fact can lead to an interesting stuff, such as that you can make a const that holds the value of the migrate variable and set it to True while development and return it to False when you’re ready to publish your work.

  • web2py DAL does not perform any hidden Database IO. You have to call count, insert, delete, update or select to do any IO. This is a feature, not a limitation.
    At the current time no need for an ORM on top of it because the current DAL is more usable then existing ORMs.
  • Web2py DAL makes a good work for preventing uncompleted commitments to database to ruin your data
    All calls are wrapped into a transaction, and any uncaught exception
    causes the transaction to roll back. If the request succeeds, the trans-
    action is committed.
  • DAL supports distributed transactions
  • Web2py DAL provides us with some interesting stuff that makes your life easier :
    • db().select(db.table_name.field, orderby='<random>')
      
      You can get a random order every time the query is initiated.</li>
      
      
      <li>
      db._lastsql -> returns the last sql code generated by DAL
      
    • most web2py expressions can easily be serialized in SQL. For example:
      myquery=(db.table.field==value)|(db.table.id>10)
      

      Warning Warning Warning :
      Always use when ever doing queries the operators ‘&’, ‘|’ , Don’t use ‘and’, ‘or’ .

    • you can print str(myquery) and see the SQL that corresponds to the
      query.
    • methods :
       .delete(), .update(), .insert() and .select() 
      

      they all have a :

      ._delete(), ._update(), ._indert(), ._select()
      

      that instead of performing the operation return the SQL that does.

    • You can list all tables in database using : db.tables() which leads to some interesting stuff like:
      db.define_table('rating', Field('table_name'), Field('record_id', 'integer'), Field('rate', 'integer'))
      
      db.rating.table_name.requires = IS_IN_SET(db.tables())
      

      and whenever trying to insert some record you can do something like:

      db.rating.insert(table_name = str(db.game), record_id=..., rate=...)
      
    • DAL supports ‘NOT’ using the ‘~’, so you can do something like:

      db( ~db.table.field.belongs((1,2,3))).select() 
      
    • Web2py’s DAL supports limitby for pagination.Supporting limitby in oracle was a problem since oracle doesn’t support it.
      Both web2py and Django support this feature differently, While the code generated by Django is more readable, it is slower
      because it asks Oracle to first select all rows, then select the
      limited subset. The web2py way does it with three nested select that,
      as discussed in This article , allows Oracle to perform additional optimizations (and it works with joins too).
  • web2py’s Database Abstraction Layer (DAL) supports unicode by default
    you can check for that in gluon/sql.py

            charset = m.group('charset') or 'utf8'
             self._pool_connection(lambda : MySQLdb.Connection(
                        db=db,
                        user=user,
                        passwd=passwd,
                        host=host,
                        port=int(port),
                        charset=charset,
                        ))
            .........................................
            .........................................
            # table should use this utf-8 when creating it
            if self._db._dbname == 'mysql':
                fields.append('PRIMARY KEY(%s)' % self.fields[0])
                other = ' ENGINE=InnoDB CHARACTER SET utf8;'
    
  • To deal with oracle database, web2py needs cx_Oracle
  • single quotes are escaped in Oracle SQL using repeated single quotes and web2py takes care of this
  • DAL makes a great job in simplifying selecting from database, so you can do :
    db(db.my_table.id>0).select()
    or
    db((db.my_table.id>0) & (db.my_table.second_field == 'value') ).select()
    or even easier :
    db(db.my_table.id>0)(db.my_table.second_field == 'value').select()
    
    so:
    db(a)(b)(c) is the same as db((a)&(b)&(c))
    in fact the former is interpreted as taking the (c) subset of the (b)  
    subset of the (a) subset of db. 
    
  • dropping a database table manually causes web2py to fail and not working, with an error message that table doesn’t exist? while this doesn’t happen in case of dropping the table through web2py and the reason for this is :
    • when tables are created the first time web2py makes a .table file under applications/yourapp/databases
      that is how keeps track of table structure.
    • If you drop the tables manually, you need to delete those files as well or they will not be re-created.
  • You can make 2 web2py’s applications share the same database, you can copy the model files within database tables are defined to another application and start to use it.
    One proble though is that there should be only one application that is allowed to create tables and the other should have ‘migrate=False’ s the last argument in db.defin_table()

    Web2py keeps track of the migration files in a folder called database, web2py generates a random name for it and you should [if you tend set migration to True to give it a name]

    migrate='table_name.table'   => '%s.table'%table_name
    

    if the database is re-factored with a name change, we wouldn’t want to lose the data from the column, just have the column name changed
    So what to do?

    Find the .table file for that table and set migrate= to that filename.
    One should actually use migrate=”mytable.table” to give a name to the table files from the beginning create instead of sing the cryptic
    names created vy web2py.

  • You can’t reference other tables using other fields than their id, which is a good practice and in the same time efficient (strings need to be hashed while integers don’t. )

  • Dal has some limitations though:
    • Doesn’t support inheritance, and although you can do something like:
      db.define_Table('my_table', ....)
      db.new_table = db.my_table
      

      There’s no sync between them, changes in one of them are not reflected in the other.

    • Doesn’t support multiple insertion in the same query.
    • No support for special field types(Enum, Array e.t.c) and XML fields in POSTGRESQL.
    • You can’t rename a column, if you renamed it in your model, this will drop the old and create a new empty one [in case migration=True].
      To rename a column, just :
      1)create the new column.
      2)drop the old one.
      3)copy data
    • No support for self referencing foreign key [No parent/child relationship support], instead you can make an integer field and us it to store a self referencing key, with the parent field has the value of this field set to NUll or -1.
    • many-to-many relationship in web2py has to be explicit (as in rails, not as in Django). This means you have to create the intermediate link table.
      The intermediate table in a many-2-many relation, in the general case, can hold more than two keys.
      You can use sqldesigner, but you need to create the intermediate table to link the many- to the -many.
    • DAL doesn’t support something like :
      table A depends on table B
      table B depends on table C
      table C depends on table A
      
  • In web2py, menus can be created automatically :
    • check menu.py in your models in your web application folder
    • you can also check for the current used action in a menu [To make an active item]
      response.menu=[
      ['item name',(request.function=='action'), URL(r=request,f='action',vars={}, args=[])],
      ]
      

      as you can see you check with request.function==’action’ where ‘action’ is the name of the function called [change it to the name of the controller function that is referred to by this menu item]

  • Making a private function is easy in web2py :
    • Functions defined in a model are private.
    • Functions that are defined in controllers and that takes arguments are private.
    • Functions defined in controllers and start with ‘__’ [double underscores] are private.
      But functions starting with single ‘_’ are not private and they should not be because some people use them for an ajax callback.
    • Functions defined in controllers and having a space after the () and before the ‘:’ are private.
      ex:

      def pri_action() :
      # do some thing
      
  • web2py provide us with many many HTML helpers that makes your life easier and instead of writing an HTML code all the time, you can use them as [python code] either in the view or in your controller functions (actions) .
    They do a grat job and makes you use python instead of HTML code in your actions.

    A('Download', _href=URL(....)) instead of <a href=''>'Download'</a>
    

    You can also have a server side highlighting using CODE helper that will display code in HTML with highlighting.

     {{=CODE(\"print 'hello world'\", language='python', link=None,
                counter=1, styles={})}}
    

    another example:

    BR -> <br/>
    
    P(..., cr2br=True)  Will replace ``\\n`` by ``<br />`` if the `cr2br` attribute is provided.
    
    P() -> <p>
    
  • You need to know that the philosophy of web2py HELPERS is:
    • Not to deliver all possible HTML helpers since it’s very easy to do a one , just look at gluon.html.py and you’ll see how easy it is
      you just make a class that extends the DIV class and into it you type
      tag = ‘whatever tag you want to implement’ .
      ex:

      class FIELDSET(DIV):
          tag = 'fieldset'
      

      The fieldset tag should just wrap whatever is in it, since most designers never use tables to format forms.
      The fieldset tag helps create visible rubrics with very large forms

  • In web2py, you can return result to a user while making some computation that takes longer time.
    • For this don’t use forking because it doesn’t work in windows.
    • If the computation can be interrupted you can have an ajax call from
      the client initiate the computation in a separate controller function.
    • If the computation can not be interrupted I would run it a separate
      thread (not process). Mind that wsgiserver will kill threads that run
      too long.