Programmatically copying ActiveModel validators from one model to another?

[John Feminella]

I'm writing a library that will require programmatically copying validations from one model to another, but I'm stumped on how to pull this off.

I have a model that is an `ActiveModel::Model` with some validation:

    class User < ActiveRecord::Base

      validates :name, presence: true

    end

And another model that I'd like to have the same validations:

    class UserForm

      include ActiveModel::Model

      attr_accessor :name

    end

Now I'd like to give `UserForm` the same validations as `User`, and without modifying `User`. Copying the validators over doesn't work, because `ActiveModel::Validations` hooks into callbacks during the validation check:

    UserForm._validators = User._validators

    UserForm.new.valid?

    # => true             # We wanted to see `false` here, but no validations

                          # are actually running because the :validate callback

                          # is empty.

Unfortunately, there doesn't seem to be an easy way that I can see to programmatically give one model another's validation callbacks and still have it work. I think my best bet is if I can ask Rails to regenerate the validation callbacks based on the validators that are present at a given moment in time.

Is that possible? If not, is there a better way to do this?

[and...@benjamin.dk]

Why don't you try creating a concern and decorate the class with that concern that contains the validations?

you can have a look here: http://stackoverflow.com/questions/11372484/rails-put-validation-in-a-module-mixin and here: http://blog.andywaite.com/2012/12/23/exploring-concerns-for-rails-4/

does this needs to be done in run time?

hope it helps.