So I have this question:
Suppose I have these 3 models:
class Company < ActiveRecord::Base has_many :departments has_many :employees end
class Department < ActiveRecord::Base has_many :employees belongs_to :company end
class Employee < ActiveRecord::Base belongs_to :company belongs_to :department end
Furthermore, suppose the domain I am modeling requires that I support the existence of employees that do not belong to any department (otherwise I would declare that Company has_many :employees, :through => :departments instead).
As I am working with the Department model, I am thinking that it is conceivable that a mistake can be made in the code to allow an employee from a company to be incorrectly assigned to a department in another company. Hence, it might be a good idea to write some custom validation to ensure an employee and a department belong to the same company before they associated together.
Since associate a department and an employee together in one of two ways, I would need validation logic in both models. So I am thinking it would involve something like:
1. In the Department model
def validate self.errors.add(:employees, "must all belong to same company") if self.employees.collect { |e| e.company_id }.uniq.length > 1 end
2 In the Employee model:
def validate self.errors.add(:department, "must belong to the same company") if self.department && self.department != self.company end
However, having to write two separate methods to support a single business rule feels not so DRY or elegant. Is there a better way to go?
Thanks!
