Rails 4-基于多种模型的验证

Question

I have USERS, CATEGORIES and WORKGROUPS. A user belongs to a workgroup: user.workgroup_id. A category belongs to a workgroup: category.workgroup_id. WORKGROUP has many users and categories.

I need to write a model validation that disallows assigning a category.workgroup_id where no existing user has that particular workgroup_id, with an error message like, "Sorry, but no one belongs to that workgroup, so you may not assign it to this Category."

Any advice? Thanks in advance.

Answer 1

class Category < ActiveRecord::Base
  belongs_to :workgroup

  validate :workgroup_not_empty, if: Proc.new { workgroup_id_changed? }

  def workgroup_not_empty
    if workgroup.users.count == 0
      errors.add(:workgroup_id, "Sorry, but no one belongs to that workgroup, so you may not assign it to this Category.")
    end
  end
end