Rails - May 2008 - Adding validations on the fly.

Hello,

In some situations I''d like to extend single objects with additional
virtual attributes and validation methods for them, for example:

@foo = Foo.find(param[:id])

class << @foo
  def bar
    nil
  end

  validates_presence_of :bar
end

puts @foo.valid?

However, what is puzzling is that this still returns true... Can anyone
point me at what I''m doing wrong?
-- 
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On Tuesday 13 May 2008, Krzysztof Wrzalik wrote:
> Hello,
>
> In some situations I''d like to extend single objects with
additional
> virtual attributes and validation methods for them, for example:
>
> @foo = Foo.find(param[:id])
>
> class << @foo
>   def bar
>     nil
>   end
>
>   validates_presence_of :bar
> end
>
> puts @foo.valid?
>
> However, what is puzzling is that this still returns true... Can
> anyone point me at what I''m doing wrong?
Your call to validates_presence_of addss a validation on the singleton 
class of @foo where it will never be executed. You''d need to add the 
validation to the class Foo

  @foo.class.validates_presence_of :bar

but then it would be active for all instances of Foo in the same 
process. Much better to add the validation to the class proper and 
guard it with a condition

  class Foo < ActiveRecord::Base
    validates_presence_of :bar, :if => ...
  end

Michael

-- 
Michael Schuerig
mailto:michael-q5aiKMLteq4b1SvskN2V4Q@public.gmane.org
http://www.schuerig.de/michael/

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