Easier Non ActiveRecord models in Rails 4

Rails 4 introduces a nice new feature for dealing with non-ActiveRecord models. These kinds of models can be useful in a situation where you have a class that you want to function like a typical ActiveRecord model, but you have no need to persist it to the database. I’ve done this on a few occasions with contact forms, for example.

Where previously you might have set up a model that looked something like this, with active model pieces being brought in to the class individually, a class constructor to set up attributes, as well as some random methods required to make it work, the persisted? method shown below, for example:

class Contact
  extend ActiveModel::Naming
  include ActiveModel::Conversion
  include ActiveModel::Validations

  attr_accessor :email, :message

  validates :email, presence: true, length: {in:2..255}

  def initialize(attributes = {})
    self.attributes = attributes
  end

  def attributes=(attributes)
    @email = attributes[:email]
    @message = attributes[:message]
  end
  private :def_attributes

  def persisted?
    false
  end

end

Rails 4 introduces ActiveModel::Model, which could clean up the above class to look something like this:

class Contact
  include ActiveModel::Model

  attr_accessor :email, :message

  validates :email, presence: true, length: {in:2..255}

end

In this example, the class constructor which was being used to initialze the object with an attribute hash been removed; the persisted? method is no longer necessary; the various ActiveModel includes have been reduced to a one-liner. Depending on what bits you’ve needed from ActiveModel, it may have other benefits.

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May 8, 2014

Easier Non ActiveRecord models in Rails 4