Nil Returning ActiveRecord::Coders::YAMLColumn

nil_returning_coder.rb

require 'active_record/coders/yaml_column'
require 'active_support'
require 'yaml'
# This module defines an YAMLColumn coder that returns 
#   nil instead of a blank object.  Useful when the class you are serializing
#   to/from does not allow uninitialized objects (such as a unit measurement)
#
# See more: http://blog.deanbrundage.com/2012/10/rails-serialization-of-nil-values/
#
module NilReturningCoder

  extend ActiveSupport::Concern

  module ClassMethods
    def dump(obj)
      Coder.new.dump(obj)
    end
    def load(yaml)
      Coder.new.load(yaml)
    end
  end

private

  class Coder < ActiveRecord::Coders::YAMLColumn
    def dump(obj)
      return if obj.nil?
      super
    end
    def load(yaml)
      return if yaml.nil?
      super
    end
  end

end

nil_returning_coder_spec.rb

Blark = Struct.new(:attr) do
  include NilReturningCoder
end

describe NilReturningCoder do

  let(:klass)  { Blark }
  let(:object) { klass.new }
  let(:coder)  { NilReturningCoder::Coder.new }

  shared_examples_for 'a dumper' do
    it 'returns nil when given nil' do
      dumper.dump(nil).should be_nil
    end
    it 'returns yaml when given something' do
      dumper.dump(object).should eq object.to_yaml
    end
  end


  shared_examples_for 'a loader' do
    it 'returns nil when given nil' do
      loader.load(nil).should be_nil
    end
    it 'returns the object when given yaml' do
      loader.load(object.to_yaml).should eq object
    end
  end


  describe :ClassMethods do

    [:dump, :load].each do |meth|
      it "mixes in #{meth}" do
        klass.should respond_to(meth)
      end
    end

    it_behaves_like 'a dumper' do
      let(:dumper) { klass }
    end

    it_behaves_like 'a loader' do
      let(:loader) { klass }
    end

  end

  describe :Coder do

    it_behaves_like 'a dumper' do
      let(:dumper) { coder }
    end

    it_behaves_like 'a loader' do
      let(:loader) { coder }
    end

  end

end