Rails: In Rails how to use the model’s Attribute API on a tableless model

Question

I have a table-less model like this:

class SomeModel
  include ActiveModel::Model
  attribute :foo, :integer, default: 100
end

I’m trying to use an attribute from the link below, it works perfectly in normal models however I cannot get it to work in a tableless model.

https://api.rubyonrails.org/classes/ActiveRecord/Attributes/ClassMethods.html

This causes an undefined

I’ve tried adding active record attributes:

include ActiveRecord::Attributes

as an include too however this causes a different error related to the schema.

How do I go about using the attribute in a tableless model? Thanks.

Answer 1

You need to include ActiveModel::Attributes

class SomeModel
  include ActiveModel::Model
  include ActiveModel::Attributes
  attribute :foo, :integer, default: 100
end

For some reason its not included in ActiveModel::Model. This internal API was extracted out of ActiveRecord in Rails 5 so you can use it with table-less models.

Note that ActiveModel::Attributes is NOT the same thing as ActiveRecord::Attributes. ActiveRecord::Attributes is a more specialized implementation that assumes the model is backed by a database schema.