With ActiveType Show archive.org snapshot 1.2 you can modify associations (has_many etc.) after they have been defined.

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One common use case for this is to change an association inside a form model, like this:

class Credential < ActiveRecord::Base
end

class User < ActiveRecord::Base
  has_many :credentials
end

class SignUpCredential < ActiveType::Record[Credential]
end

class SignUp < ActiveType::Record[User]
  change_association :credentials, class_name: 'SignUpCredential'
end

Now, if you load credentials, you will automatically receive records of type SignUpCredential.