Rails - Oct 2008 - Using an associated model in an attribute setter

Hi,
I want to use an associated model in an overwritten attribute write 
method. But this fails on create, as the association is not yet 
initialized. Code is:

class Forward < ActiveRecord::Base
  belongs_to :domain
  validates_presence_of :domain, :destination
  validates_uniqueness_of :name, :scope => :domain_id

  def destination=(dest)
      dest = dest + ''@'' + domain.name unless (domain.blank? ||
dest =~ /@/)
      write_attribute :destination, dest
  end
end

When calling destination= and then save, it works fine, put when 
calling Forward.new(attributes) from the controller, domain yields nil 
in destination=, even though domain is initialized before saving, and 
validation succeeds.

How can I achieve that destination= is executed correctly when creating 
a new Forward?
I tried the following callback in Forward:
  before_validation_on_create { |record| record.destination=record.destination}
and it seems to work. Is this correct, or might this have some side 
effects? It also seems quite hacky, is there a cleaner way?

Regards
Rainer Frey



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On 21 Oct 2008, at 15:56, Rainer Frey wrote:
>
> Hi,
> I want to use an associated model in an overwritten attribute write
> method. But this fails on create, as the association is not yet
> initialized. Code is:
>
> class Forward < ActiveRecord::Base
>  belongs_to :domain
>  validates_presence_of :domain, :destination
>  validates_uniqueness_of :name, :scope => :domain_id
>
>  def destination=(dest)
>      dest = dest + ''@'' + domain.name unless
(domain.blank? || dest
> =~ /@/)
>      write_attribute :destination, dest
>  end
> end
>
> When calling destination= and then save, it works fine, put when
> calling Forward.new(attributes) from the controller, domain yields nil
> in destination=, even though domain is initialized before saving, and
> validation succeeds.
>
> How can I achieve that destination= is executed correctly when  
> creating
> a new Forward?
Forward.new(attributes) boils down to:
- create a blank instance
- attributes.each {|k,v| object.send("#{k}=",v)

hashes are unordered so you can''t rely on domain being set before  
destination is.

Fred
>
> I tried the following callback in Forward:
>  before_validation_on_create { |record|  
> record.destination=record.destination}
> and it seems to work. Is this correct, or might this have some side
> effects? It also seems quite hacky, is there a cleaner way?
>
> Regards
> Rainer Frey
>
>
>
> >

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Frederick Cheung wrote:
> Forward.new(attributes) boils down to:
> - create a blank instance
> - attributes.each {|k,v| object.send("#{k}=",v)
> 
> hashes are unordered so you can''t rely on domain being set before
> destination is.
Ok, so I need to take care of this afterwards. Any comments on below
solution/workaround?
>> I tried the following callback in Forward:
>>  before_validation_on_create { |record|
>> record.destination=record.destination}
>> and it seems to work. Is this correct, or might this have some side
>> effects? It also seems quite hacky, is there a cleaner way?
Regards
Rainer Frey


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