# Conditional model validation

**URL:** <https://www.ruby-forum.com/t/conditional-model-validation/163676>\
**Category:** Rails\
**Created:** [March 23, 2009, 9:27pm UTC](https://www.ruby-forum.com/t/conditional-model-validation/163676 "2009-03-23T21:27:17Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![jzimmek](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/d07c76/32.png) [@jzimmek](https://www.ruby-forum.com/u/jzimmek)\
**Post date:** [March 23, 2009, 9:27pm UTC](https://www.ruby-forum.com/t/conditional-model-validation/163676/1 "2009-03-23T21:27:17Z")

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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

---

<div class="post-metadata">

**Author:** ![jzimmek](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/d07c76/32.png) [@jzimmek](https://www.ruby-forum.com/u/jzimmek)\
**Post date:** [March 23, 2009, 10:19pm UTC](https://www.ruby-forum.com/t/conditional-model-validation/163676/2 "2009-03-23T22:19:00Z")

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On Mar 23, 8:26 pm, jzimmek [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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 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