What fields_for really for?

Hello everyone!
I have 3 models:
=== 1 ===
class Region < ActiveRecord::Base
has_many :districts
end
=== 2 ===
class District < ActiveRecord::Base
belongs_to :region
has_many :suburbs
end
=== 3 ===
class Suburb < ActiveRecord::Base
belongs_to :district
validates_numericality_of :region_id, :only_integer => true
end

In edit.rhtml for SuburbController I need to specify region_id.
There is no region_id in suburb model so first I added these lines to
it:

class Suburb < ActiveRecord::Base
belongs_to :district
attr_writer :region_id
def region_id
district.region_id if district
end
def region_id_before_type_cast
region_id
end
validates_numericality_of :region_id, :only_integer => true
end

Its all working now but it looks messy! And I need this functionality in
another few places. Obviously I dont want to put this rubbish into other
models!

I recently come across fields_for helper. So I commented out
“unnecessary” code in the model, put these into view:

<% fields_for :district, @suburb.district do |district_fields| %>
<%= district_fields.select :region_id, regions %>
<% end %>

And, guess what, I still need these damn methods in my model!
Why would I use fields_for then? I don’t know!

QUESTION 1: How can I apply fields_for in my case, so I do not need to
pollute my models? Or is there any other ways?

QUESTION 2: What is it all about this “_before_type_cast” method? I mean
do I have to have it only to use validates_numericality_of? Can it be
created automatically?

Than you!

On 13/08/06, Igor Su [email protected] wrote:

QUESTION 2: What is it all about this “_before_type_cast” method? I mean
do I have to have it only to use validates_numericality_of? Can it be
created automatically?

before_type_cast methods are called for your model’s fields before they
are
type cast. Strictly speaking, I don’t think you need them. Suppose, you
have
a currency field that needs to be converted to a different currency
before
displaying. Instead of converting from a string to a float the
before_type_cast methodis passed the value as a float.

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