conditional model validation

rubyonrails-talk
1

i really like the declarative model-based validation in rails, but i run into trouble while doing some real world (more complex) stuff.

class User < ActiveRecord::Base   belongs_to :address   accepts_nested_attributes_for :address   def needs_street_validation?     true   end end

class Address < ActiveRecord::Base   has_one :user   validates_presence_of :street, :if => Proc.new { |adr| adr.user.needs_street_validation? } end

u = User.new u.address = Address.new u.save

NoMethodError: You have a nil object when you didn't expect it! The error occurred while evaluating nil.needs_street_validation?         from app/models/address.rb:3

seems to me like we cannot reference any associated object within the ":if" condition or do you know some trick to get this working ?

maybe this is not the best example, but i hope you got the point.

in most more-complex gui's we have conditional validation based on the state of multiple objects. It would be a shame if we could only handle those validation programmatically.

tested in a vanilla rails 2.3.2 application.

any help would be really appreciated.

regards jan

2

u = User.new u.address = Address.new u.save

NoMethodError: You have a nil object when you didn't expect it! The error occurred while evaluating nil.needs_street_validation? from app/models/address.rb:3

seems to me like we cannot reference any associated object within the ":if" condition or do you know some trick to get this working ?

The problem isn't anything to do with :if's, more a general quirk of activerecord - When you assign Address.new to u.address activerecord doesn't update the inverse assocation on the address object. In the case where you're doing this with already saved objects you can use tricks like set_#{association_name}_target to do that work of filling in the inverse association, though I don't know if the fact that your objects are unsaved makes a difference.

Fred