Conditional model validation

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?

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

u =
u.address =

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.


On Mar 23, 8:26 pm, jzimmek [email protected] wrote:

“: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 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.


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