Conditional attributes in Active Model Serializers

Question

How do I render an attribute only if some condition is true?

For example, I want to render User's token attribute on create action.

Answer 1

In the latest version (0.10.x), you can also do it this way:

class EntitySerializer < ActiveModel::Serializer
  attributes :id, :created_at, :updated_at
  attribute :conditional_attr, if: :condition?

  def condition?
    #condition code goes here
  end
end

For example:

class UserSerializer < ActiveModel::Serializer
  attributes :id, :username, :name, :email, :created_at, :updated_at
  attribute :auth_token, if: :auth_token?

  def created_at
    object.created_at.to_i
  end

  def updated_at
    object.updated_at.to_i
  end

  def auth_token?
    true if object.auth_token
  end
end

EDIT (Suggested by Joe Essey) :

This method does not work with latest version (0.10)

With the version 0.8 it is even simpler. You don't have to use the if: :condition?. Instead you can use the following convention to achieve the same result.

class EntitySerializer < ActiveModel::Serializer
  attributes :id, :created_at, :updated_at
  attribute :conditional_attr

  def include_conditional_attr?
    #condition code goes here
  end
end

The example above would look like this.

class UserSerializer < ActiveModel::Serializer
  attributes :id, :username, :name, :email, :created_at, :updated_at
  attribute :auth_token

  def created_at
    object.created_at.to_i
  end

  def updated_at
    object.updated_at.to_i
  end

  def include_auth_token?
    true if object.auth_token
  end
end

See 0.8 documentation for more details.