Rails old migrations fail due to validation in model for new column

Question

I have an application using active admin with devise in production. I try to add user_role to the table admin_users. I also want to validate if the role name is chosen when creating a new admin user. so I add validates :role_id, :presence => true in rails model.

When I run my new migrations on the old database, everything works fine. But when I try to apply the migrations from scratch, the old migration for creating admin user fails because of the validation added in a model, saying undefined method error.

Without changing the old migrations and by having the validation when creating admin users from UI, Is it possible to overcome this situation

Answer 1

I have faced this issue and the best solution to me seems to be to modify the model inside the migration and remove the problematic validation (for the duration of the migration) by opening the model's class.

Let's say you have a model Employee and a validation on a column firstname is interfering with a particular migration. Assuming you're using Rails 4.2, this should work:

class CreateStoreFromPreferences < ActiveRecord::Migration
  def change
    Employee.class_eval do
      _validators.delete(:firstname)

      _validate_callbacks.each do |callback|
        if callback.raw_filter.respond_to? :attributes
          callback.raw_filter.attributes.delete :firstname
        end
      end
    end

    # actual migration code goes here
  end
end