how to perform validation prior to creating a new association between records?

[coriordan]

Hi,

I'm trying to figure out the correct "Rails" way to perform validation prior to creating a new assocation between my models. Here's the models:

class User < ActiveRecord::Base
 
  has_and_belongs_to_many :roles
  has_many :instructorships
  has_many :instructed_courses, :through => :instructorships, :source => :course

class Course < ActiveRecord::Base
 
  has_many :instructorships
  has_many :instructors, :through => :instructorships, :source => :instructor

class Instructorship < ActiveRecord::Base
  belongs_to :instructor, :class_name => 'User', :foreign_key => 'user_id'
  belongs_to :course

I'm trying to introduce a validation whereby only user objects with a role of 'instructor' can be assigned as an instructor on a course.

Firstly, where would this validation go? On the association model? And secondly, what is the right way to set this up?

thanks for your help,
Cathal.

[Dheeraj Kumar]

The validation would go in the Instructorship model.

You'll need a custom method, like so: http://edgeguides.rubyonrails.org/active_record_validations.html#custom-methods

-- 

Dheeraj Kumar

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[coriordan]

Thanks Dheeraj :)