Rails - Mar 2006 - Validating that a foreign key is present and ok

How do I validate that a model object''s attribute is a valid foreign
key? The problem is, I can''t check if the attribute is a valid foreign
key if the attribute doesn''t even exist.

For example, every employee must be in a department. In the following
code, if an employee''s department_id is not present then
Department.find_by_id(department_id) might cause problems, yes?


class Employee < ActiveRecord::Base
  validates_presence_of :department_id
  def validate
    errors.add(:department_id) unless Department.find_by_id(department_id)
  end
end

department_id should be present, a positive integer, and a valid
foreign key to the departments table. This is a common thing to want
to validate. How do you do it?

Thanks,
Peter

Peter Michaux wrote:
> How do I validate that a model object''s attribute is a valid
foreign
> key? The problem is, I can''t check if the attribute is a valid
foreign
> key if the attribute doesn''t even exist.
> 
> For example, every employee must be in a department. In the following
> code, if an employee''s department_id is not present then
> Department.find_by_id(department_id) might cause problems, yes?
> 
> 
> class Employee < ActiveRecord::Base
>   validates_presence_of :department_id
>   def validate
>     errors.add(:department_id) unless Department.find_by_id(department_id)
>   end
> end
> 
> department_id should be present, a positive integer, and a valid
> foreign key to the departments table. This is a common thing to want
> to validate. How do you do it?
All you need is "validates_presence_of :department".

-- 
We develop, watch us RoR, in numbers too big to ignore.

On 3/1/06, Mark Reginald James <mrj@bigpond.net.au>
wrote:
> All you need is "validates_presence_of :department".
Why? When is the validity of the foreign key checked? What error
message does it add?