Rails - Oct 2006 - Why don't form helpers read custom model attributes ?

Hi!

I''m using custom read and write accessors in my models like :

class Order < ActiveRecord::Base

...

def date
  read_attribute(:date).strftime(''%d/%m/%Y'')
end

...

end

My problem is that Form helpers like text_field, text_area, etc, don''t 
seem to work with these custom accessors, is that normal ?

Thanks!

Nicolas.

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Nicolas Blanco wrote:
> Hi!
> 
> I''m using custom read and write accessors in my models like :
> 
> class Order < ActiveRecord::Base
> 
> ...
> 
> def date
>   read_attribute(:date).strftime(''%d/%m/%Y'')
> end
> 
> ...
> 
> end
> 
> My problem is that Form helpers like text_field, text_area, etc,
don''t
> seem to work with these custom accessors, is that normal ?
> 
> Thanks!
> 
> Nicolas.

The form helpers should be able to read all of the methods on the model. 
My first guess was that the helper was grabbing the date attribute 
instead of your date method, but that doesn''t sound possible to me
since
your method should be triggered first.  My second guess is that perhaps 
it won''t use an accessor unless it also has a setter ( ex. a method 
named date=(new_date) ).  Those are just guesses though... if you tried 
creating a differently named method, or adding a setter, it would be 
easy enough to test out.

Tom

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It always seems to go right to the backend, skipping your code. I run into
this often.

My solution is this:

attr_writer :date_for_form

def date_for_form
  read_attribute(:date).strftime(''%d/%m/%Y'')
end

before_validate :copy_form_fields

def copy_form_fields
   self.attributes(:date) = self.date_for_form
end


Warning: untested. Write a unit test for this before you implement it :)

This should allow you to use the form helpers on your new fields
(date_for_form)  Kinda kludgy but it will get you going.

On 10/27/06, Nicolas Blanco <
rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
>
>
> Hi!
>
> I''m using custom read and write accessors in my models like :
>
> class Order < ActiveRecord::Base
>
> ...
>
> def date
>   read_attribute(:date).strftime(''%d/%m/%Y'')
> end
>
> ...
>
> end
>
> My problem is that Form helpers like text_field, text_area, etc,
don''t
> seem to work with these custom accessors, is that normal ?
>
> Thanks!
>
> Nicolas.
>
> --
> Posted via http://www.ruby-forum.com/.
>
> >
>

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Nicolas Blanco wrote:
> I''m using custom read and write accessors in my models like :
> 
> class Order < ActiveRecord::Base
> 
> ...
> 
> def date
>   read_attribute(:date).strftime(''%d/%m/%Y'')
> end
> 
> ...
> 
> end
> 
> My problem is that Form helpers like text_field, text_area, etc,
don''t
> seem to work with these custom accessors, is that normal ?

In order to preserve both database field formats and redisplayed
user input, AR form helpers get their display strings from
<attribute>_before_type_cast methods.

So you could write:

def date_before_type_cast
   date.strftime(''%d/%m/%Y'')
end

But if you want a common date display format throughout your app,
instead add

ActiveSupport::CoreExtensions::Date::Conversions::DATE_FORMATS[:default] =
''%d/%m/%Y''

to environment.rb, and write in your model

def date_before_type_cast
   date.to_s
end


You''ll also need a setter

def date=(val)
   self[:date] = val.is_a?(String) ? val.to_date : val
end

plus, since Rails does not currently support non-US formats for
string-to-date conversions, you''ll have to add this to environment.rb

class String
   def to_date
     Date.strptime(self, ''%d/%m/%Y'')
   end
end

-- 
We develop, watch us RoR, in numbers too big to ignore.


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Mark Reginald James wrote:
> Nicolas Blanco wrote:
>
> > I''m using custom read and write accessors in my models like :
> >
> > class Order < ActiveRecord::Base
> >
> > ...
> >
> > def date
> >   read_attribute(:date).strftime(''%d/%m/%Y'')
> > end
> >
> > ...
> >
> > end
> >
> > My problem is that Form helpers like text_field, text_area, etc,
don''t
> > seem to work with these custom accessors, is that normal ?
>
>
> In order to preserve both database field formats and redisplayed
> user input, AR form helpers get their display strings from
> <attribute>_before_type_cast methods.
>
> So you could write:
>
> def date_before_type_cast
>    date.strftime(''%d/%m/%Y'')
> end
>
> But if you want a common date display format throughout your app,
> instead add
>
> ActiveSupport::CoreExtensions::Date::Conversions::DATE_FORMATS[:default] =
''%d/%m/%Y''
>
> to environment.rb, and write in your model
>
> def date_before_type_cast
>    date.to_s
> end
>
>
> You''ll also need a setter
>
> def date=(val)
>    self[:date] = val.is_a?(String) ? val.to_date : val
> end
>
> plus, since Rails does not currently support non-US formats for
> string-to-date conversions, you''ll have to add this to
environment.rb
>
> class String
>    def to_date
>      Date.strptime(self, ''%d/%m/%Y'')
>    end
> end
>
> --
> We develop, watch us RoR, in numbers too big to ignore.
I strongly recommend that you DO NOT CHANGE THE DEFAULT DATE FORMAT.
This will lead to unending pain and suffering, and will highly
displease the gods of MySQL.

If you change the default date format, rails will use this format to
try and write dates to the db.  Mostl likely this will result in a
silent failure (at least in MySQL).  Your dates will just get recorded
as ''0000-00-00'', and you will lose fistfuls of hair trying to
figure
out why. 

See tickets #6019 and #6363

_Kevin


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Nicolas Blanco wrote:
> My problem is that Form helpers like text_field, text_area, etc,
don''t
> seem to work with these custom accessors, is that normal ?
> 
> Thanks!
> 
> Nicolas.
Nicolas,

Yes, this is normal.  And for whatever it''s worth, I''ve
learned and
forgotten this at least 3 times - since I''m thinking in pure OO mode 
most of the time and I expect overridden methods to get called.

Because you can do complex transformations in a custom attribute reader, 
Rails gets the attribute value using _before_type_cast.

One way to think about the reason for this is because Rails has no 
built-in notion of a model of the form''s state (what in the J2EE world 
might be called a "form bean").  Because the default behavior of the 
ActiveRecord/controller/view interaction is to read/write attributes 
directly from the DB to/from the view, there''s no facility to keep
track
of what''s going on the form during unsuccessful attempts to save a 
particular attribute (e.g. what was typed into the form field when it''s
not valid).

In effect, you end up using a custom attribute reader/writer pair to 
manage this form state.  If you take the set of all such methods that 
you end up writing on your ActiveRecord object, you would see that they 
basically represent a "form state" or "form model" object,
even though
they are methods on the model.

I''ve been thinking about this a lot.  Take a look at the ActiveForm 
plugin for one way to formalize this "form model" notion.  In cases 
where the form state can be complex, a separate form model would keep 
your form state straight, but then would imply a copying step from the 
form model attributes into the model attributes and the opposite.

If most of your model attributes don''t need tweaking to be displayed, 
then just adding a couple of custom attribute reader/writer pairs is 
probably sufficient.

But I think it''s helpful to keep the distinction between form data 
concerns and model data concerns in mind.

Wes

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