thr3ads.net - Rails - form question [May 2007]

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Bill Kocik

2007-May-19 20:44 UTC

form question

Suppose I have the following models/migrations:


class Car < ActiveRecord::Base
  belongs_to :manufacturer
  validates_presence_of :manufacturer
  validates_association :manufacturer
end

class CreateCars < ActiveRecord::Migration
  def self.up
    create_table cars do |t|
      t.column :name, :string
     t.column :manufacturer_id, :integer
  end
end

class Manufacturer < ActiveRecord::Base
  has_many :cars
end

class CreateManufacturers < ActiveRecord::Migration
  def self.up
    create_table maufacturers do |t|
      t.column :name, :string
    end
end

Now, I need a form to create new Cars that has two text fields: name,
and manufacturer. I can''t use a select for manufacturer, because there
are far too many of them (let''s pretend). What I can''t figure
out is
how to construct the text_field helper tag in my form such that Rails
understands that the form field doesn''t map directly to a field in the
Car object, but rather to the name field of the car''s Manufacturer
object. Is there even a way to do it? I''m looking for something like
one of these (neither of which work, obviously, but they may help to
clarify what I''m trying to do):

<%= text_field ''car'',
''car.manufacturer.name'' %> or
<%= text_field ''car'',
''car.manufacturer[:name]'' %>

Without the ability to do that, I''m not sure how I could have - for
example - an edit form without writing special code to populate that
field, or how any of the validates_* methods would work. I''ve tried
using fields_for, but it doesn''t work; probably because I''m
not doing
it right. Maybe someone knows how to use fields_for to accomplish the
above? I think what I tried was something like this:

<% fields_for :manufacturer, @car.manufacturer do |m_field| %>
<%= m_field.text_field :name %>
<% end %>

-- 
Bill Kocik

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dasil003

2007-May-19 22:44 UTC

head link

Re: form question

One thing you can do is define a pair of methods on the car object
something like this (off the top of my head).

def manufacturer_name=(value)
  manufacturer.create(:name => value)
end

def manufacturer_name
  manufacturer.name
end

On May 19, 2:44 pm, "Bill Kocik"
<bko...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> Suppose I have the following models/migrations:
>
> class Car < ActiveRecord::Base
>   belongs_to :manufacturer
>   validates_presence_of :manufacturer
>   validates_association :manufacturer
> end
>
> class CreateCars < ActiveRecord::Migration
>   def self.up
>     create_table cars do |t|
>       t.column :name, :string
>      t.column :manufacturer_id, :integer
>   end
> end
>
> class Manufacturer < ActiveRecord::Base
>   has_many :cars
> end
>
> class CreateManufacturers < ActiveRecord::Migration
>   def self.up
>     create_table maufacturers do |t|
>       t.column :name, :string
>     end
> end
>
> Now, I need a form to create new Cars that has two text fields: name,
> and manufacturer. I can''t use a select for manufacturer, because
there
> are far too many of them (let''s pretend). What I can''t
figure out is
> how to construct the text_field helper tag in my form such that Rails
> understands that the form field doesn''t map directly to a field in
the
> Car object, but rather to the name field of the car''s Manufacturer
> object. Is there even a way to do it? I''m looking for something
like
> one of these (neither of which work, obviously, but they may help to
> clarify what I''m trying to do):
>
> <%= text_field ''car'',
''car.manufacturer.name'' %> or
> <%= text_field ''car'',
''car.manufacturer[:name]'' %>
>
> Without the ability to do that, I''m not sure how I could have -
for
> example - an edit form without writing special code to populate that
> field, or how any of the validates_* methods would work. I''ve
tried
> using fields_for, but it doesn''t work; probably because
I''m not doing
> it right. Maybe someone knows how to use fields_for to accomplish the
> above? I think what I tried was something like this:
>
> <% fields_for :manufacturer, @car.manufacturer do |m_field| %>
> <%= m_field.text_field :name %>
> <% end %>
>
> --
> Bill Kocik

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Bill Kocik

2007-May-19 23:30 UTC

head link

Re: form question

On May 19, 6:44 pm, dasil003
<gabrie...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> One thing you can do is define a pair of methods on the car object
> something like this (off the top of my head).
>
> def manufacturer_name=(value)
>   manufacturer.create(:name => value)
> end
>
> def manufacturer_name
>   manufacturer.name
> end
Won''t manufacturer.create store a new manufacturer in the
manufacturers table? In my case, they''re all pre-defined. Users
populating this form aren''t creating a new one, they''re typing
the
name of one that should already exist, after which I validate.

But on that note, I did try something like this:

def manufacturer=(m)
   if m.instance_of? String
    self.manufacturer = Manufacturer.find_by_name(m)
  else
    self.manufacturer = m
  end
end

Of course, this resulted in an endless loop. Woops.

-Bill Kocik


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Bill Kocik

2007-May-20 00:27 UTC

head link

Re: form question

On May 19, 7:30 pm, Bill Kocik
<bko...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> On May 19, 6:44 pm, dasil003
<gabrie...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > One thing you can do is define a pair of methods on the car object
> > something like this (off the top of my head).
>
> > def manufacturer_name=(value)
> >   manufacturer.create(:name => value)
> > end
>
> > def manufacturer_name
> >   manufacturer.name
> > end
>
> Won''t manufacturer.create store a new manufacturer in the
> manufacturers table? In my case, they''re all pre-defined.
Actually, you''ve pretty much nailed it. I set my form up like:

<%= text_field_for ''car'',
''manufacturer_name'' %>

And in Car:

def manufacturer_name=(m)
  self.manufacturer = Manufacturer.find_by_name(m)
end

def manufacturer_name
   self.manufacturer.name
end

This seems to do pretty much exactly what I was trying to accomplish,
and my validates_presence_of works. The only thing that doesn''t work
is validates_associated :manufacturer, because when an invalid
manufacturer name is entered it isn''t found in the database, so
manufacturer remains nil and the validates_presence_of fails instead.
But I can live with that.

Thanks for the brain kick. :)

-Bill


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