class ActiveModelSerializers::Adapter::JsonApi::Relationship

def data_for(association)
  serializer = association.serializer
  if serializer.respond_to?(:each)
    serializer.map { |s| ResourceIdentifier.new(s, serializable_resource_options).as_json }
  elsif (virtual_value = association.options[:virtual_value])
    virtual_value
  elsif serializer && serializer.object
    ResourceIdentifier.new(serializer, serializable_resource_options).as_json
  end
end