Multiparameter Attributes support in Mongoid 4 (Rails 4.0.1) Code is taken from https://github.com/mongoid/mongoid/issues/2954 with minor amendments to work with Rails 4.0.1

multi-parameter_attributes_spec.rb

# This class is needed since Mongoid doesn't support Multi-parameter
# attributes in version 4.0 before it's moved to active model in rails 4
#
# https://github.com/mongoid/mongoid/issues/2954
#

require "spec_helper"
require 'mongoid/multi_parameter_attributes'

describe Mongoid::MultiParameterAttributes do

  describe "#process" do

    class Multi
      include Mongoid::Document
      include Mongoid::MultiParameterAttributes
      field :created_at, type: Time
      field :dob, type: Date
      field :checked_at, as: :last_user_checked_at, type: Time
    end

    context "creating a multi" do

      let(:multi) do
        Multi.new(
          "created_at(1i)" => "2010",
          "created_at(2i)" => "8",
          "created_at(3i)" => "12",
          "created_at(4i)" => "15",
          "created_at(5i)" => "45"
        )
      end

      it "sets a multi-parameter Time attribute correctly" do
        multi.created_at.should eq(Time.zone.local(2010, 8, 12, 15, 45))
      end

      it "does not leave ugly attributes on the model" do
        multi.attributes.should_not have_key("created_at(1i)")
      end
    end

    context "creating a multi" do

      context "with a valid DOB" do

        let(:multi) do
          Multi.new({
            "dob(1i)" => "1980",
            "dob(2i)" => "7",
            "dob(3i)" => "27"
          })
        end

        it "sets a multi-parameter Date attribute correctly" do
          multi.dob.should eq(Date.civil(1980, 7, 27))
        end
      end

      context "with an invalid DOB" do

        let(:invalid_multi) do
          Multi.new({
            "dob(1i)" => "1980",
            "dob(2i)" => "2",
            "dob(3i)" => "31"
          })
        end

        it "uses Time's logic to convert the invalid date to valid" do
          invalid_multi.dob.should eq(Time.new(1980, 2, 31).to_date)
        end
      end
    end

    context "with a blank DOB" do

      let(:multi) do
        Multi.new(
          "dob(1i)" => "",
          "dob(2i)" => "",
          "dob(3i)" => ""
        )
      end

      it "generates a nil date" do
        multi.dob.should be_nil
      end
    end

    context "with a partially blank DOB" do

      let(:multi) do
        Multi.new(
          "dob(1i)" => "1980",
          "dob(2i)" => "",
          "dob(3i)" => ""
        )
      end

      it "sets empty date's year" do
        multi.dob.year.should eq(1980)
      end

      it "sets empty date's month" do
        multi.dob.month.should eq(1)
      end

      it "sets empty date's day" do
        multi.dob.day.should eq(1)
      end
    end

    context "with aliased field" do

      let(:multi) do
        Multi.new(
          "last_user_checked_at(1i)" => "2010",
          "last_user_checked_at(2i)" => "8",
          "last_user_checked_at(3i)" => "12",
          "last_user_checked_at(4i)" => "15",
          "last_user_checked_at(5i)" => "45"
        )
      end

      it "sets a multi-parameter Time attribute correctly" do
        multi.last_user_checked_at.should eq(Time.zone.local(2010, 8, 12, 15, 45))
      end

      it "does not leave ugly attributes on the model" do
        multi.attributes.should_not have_key("created_at(1i)")
      end
    end
  end
end

multi_parameter_attributes.rb

# This class is needed since Mongoid doesn't support Multi-parameter
# attributes in version 4.0 before it's moved to active model in rails 4
#
# https://github.com/mongoid/mongoid/issues/2954
#

# encoding: utf-8
module Mongoid

  # Adds Rails' multi-parameter attribute support to Mongoid.
  #
  # @todo: Durran: This module needs an overhaul.
  module MultiParameterAttributes

    module Errors

      # Raised when an error occurred while doing a mass assignment to an
      # attribute through the <tt>attributes=</tt> method. The exception
      # has an +attribute+ property that is the name of the offending attribute.
      class AttributeAssignmentError < Mongoid::Errors::MongoidError
        attr_reader :exception, :attribute

        def initialize(message, exception, attribute)
          @exception = exception
          @attribute = attribute
          @message = message
        end
      end

      # Raised when there are multiple errors while doing a mass assignment
      # through the +attributes+ method. The exception has an +errors+
      # property that contains an array of AttributeAssignmentError
      # objects, each corresponding to the error while assigning to an
      # attribute.
      class MultiparameterAssignmentErrors < Mongoid::Errors::MongoidError
        attr_reader :errors

        def initialize(errors)
          @errors = errors
        end
      end
    end

    # Process the provided attributes casting them to their proper values if a
    # field exists for them on the document. This will be limited to only the
    # attributes provided in the suppied +Hash+ so that no extra nil values get
    # put into the document's attributes.
    #
    # @example Process the attributes.
    #   person.process_attributes(:title => "sir", :age => 40)
    #
    # @param [ Hash ] attrs The attributes to set.
    #
    # @since 2.0.0.rc.7
    def process_attributes(attrs = nil)
      if attrs
        errors = []
        attributes = attrs.class.new
        attributes.permit! if attrs.respond_to?(:permitted?) && attrs.permitted?
        multi_parameter_attributes = {}

        attrs.each_pair do |key, value|
          if key =~ /\A([^\(]+)\((\d+)([if])\)$/
            key, index = $1, $2.to_i
            (multi_parameter_attributes[key] ||= {})[index] = value.empty? ? nil : value.send("to_#{$3}")
          else
            attributes[key] = value
          end
        end

        multi_parameter_attributes.each_pair do |key, values|
          begin
            values = (values.keys.min..values.keys.max).map { |i| values[i] }
            field = self.class.fields[database_field_name(key)]
            attributes[key] = instantiate_object(field, values)
          rescue => e
            errors << Errors::AttributeAssignmentError.new(
              "error on assignment #{values.inspect} to #{key}", e, key
            )
          end
        end

        unless errors.empty?
          raise Errors::MultiparameterAssignmentErrors.new(errors),
            "#{errors.size} error(s) on assignment of multiparameter attributes"
        end
        super(attributes)
      else
        super
      end
    end

    protected

    def instantiate_object(field, values_with_empty_parameters)
      return nil if values_with_empty_parameters.all? { |v| v.nil? }
      values = values_with_empty_parameters.collect { |v| v.nil? ? 1 : v }
      klass = field.type
      if klass == DateTime || klass == Date || klass == Time
        field.mongoize(values)
      elsif klass
        klass.new(*values)
      else
        values
      end
    end
  end
end

project.rb

require 'mongoid/multi_parameter_attributes'

class Project
  include Mongoid::Document
  include Mongoid::MultiParameterAttributes

  field :organization_uid, type: Integer
  field :owner_id, type: Integer
end