active_model_errors_serializer.rb

module ActiveModel      
  class ErrorsSerializer < Serializer
    def serialize object
      @objects_hash ||= {}

      return {} if @objects_hash.has_key?(object.object_id)

      @objects_hash[object.object_id] = object

      object.errors.to_hash.merge(object.class.reflect_on_all_associations.inject({}) { |m, assoc|

        next m unless
        object.class.respond_to?(:nested_attributes_options) &&
          object.class.nested_attributes_options.has_key?(assoc.name) &&
          assoc.validate?

        target = object.send(assoc.name)

        if assoc.collection?
          errors = {}

          target.each_with_index do |o, i|
            serialized = serialize(o)
            errors[i] = serialized unless serialized.empty?
          end
          m[assoc.name] = errors unless errors.empty?
        else
          serialized = serialize(target)
          m[assoc.name] = serialized unless serialized.empty?
        end
        m
      })
    end

    def serializable_hash
      serialize(object)
    end
  end
end