It is possible to use the new ActiveRecord::Attributes API in a PORO?

Question

I usually include ActiveModel::Model into some PORO (for example for a FormObject::SignUp). I've read about the new Rails 5 ActiveRecord::Attribute API, and I thought I will be able to use it for simpler casting, but not luck.

For example, given

class FormObject::SignUp
  include ActiveRecord::Model
  include ActiveRecord::Attributes

  attribute :birthday, :date
  validates :birthday, presence: true
end

I got an NameError: undefined local variable or method `reload_schema_from_cache' for FormObjects::SignUp:Class exception when I try to instantiate it.

It is not expected to be used standalone? Thanks

Answer 1

Rails >=5.2

This is now possible in Rails 5.2.

As of Rails 5.2 (#30985), ActiveModel::Atrributes is now available to use in POROs (at least POROs that include ActiveModel::Model)...

• Reference: https://github.com/rails/rails/issues/28020#issuecomment-456616836
• Documentation: https://www.rubydoc.info/gems/activemodel/ActiveModel/Attributes#attribute_names-instance_method

Rails <5.2

Utilizing the gem ActiveModelAttributesis the only easy way I've been able to find to do this. Depending on your use case, it will probably make sense to use that gem or take a different approach.

Here is the gem: https://github.com/Azdaroth/active_model_attributes

Side note: I got feedback that link-only answers can disappear. If this link disappears, then this answer does indeed become invalid since that will likely mean the gem dosen't exist anymore.

Answer 2

ActiveModel::Attributes is available as of Rails 5.2 (PR).

Try this:

class FormObject::SignUp
  include ActiveModel::Model
  include ActiveModel::Attributes

  attribute :birthday, :date
  validates :birthday, presence: true
end