4 files changed, 76 insertions, 0 deletions
diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index ef14e065ae..58a4694880 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -43,6 +43,7 @@ module ActiveRecord
   autoload :Explain
   autoload :Inheritance
   autoload :Integration
+  autoload :LegacyYamlAdapter
   autoload :Migration
   autoload :Migrator, 'active_record/migration'
   autoload :ModelSchema
diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index 97ce4642aa..640642e90b 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -300,6 +300,7 @@ module ActiveRecord
     #   post.init_with('attributes' => { 'title' => 'hello world' })
     #   post.title # => 'hello world'
     def init_with(coder)
+      coder = LegacyYamlAdapter.convert(self.class, coder)
       @attributes = coder['attributes']
 
       init_internals
@@ -370,6 +371,7 @@ module ActiveRecord
       coder['raw_attributes'] = attributes_before_type_cast
       coder['attributes'] = @attributes
       coder['new_record'] = new_record?
+      coder['active_record_yaml_version'] = 1
     end
 
     # Returns true if +comparison_object+ is the same exact object, or +comparison_object+
diff --git a/activerecord/lib/active_record/legacy_yaml_adapter.rb b/activerecord/lib/active_record/legacy_yaml_adapter.rb
new file mode 100644
index 0000000000..0d018d4352
--- /dev/null
+++ b/activerecord/lib/active_record/legacy_yaml_adapter.rb
@@ -0,0 +1,30 @@
+module ActiveRecord
+  module LegacyYamlAdapter
+    def self.convert(klass, coder)
+      return coder unless coder.is_a?(Psych::Coder)
+
+      case coder["active_record_yaml_version"]
+      when 1 then coder
+      else
+        if coder["attributes"].is_a?(AttributeSet)
+          coder
+        else
+          Rails41.convert(klass, coder)
+        end
+      end
+    end
+
+    module Rails41
+      def self.convert(klass, coder)
+        attributes = klass.attributes_builder
+          .build_from_database(coder["attributes"])
+        new_record = coder["attributes"][klass.primary_key].blank?
+
+        {
+          "attributes" => attributes,
+          "new_record" => new_record,
+        }
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/yaml_serialization_test.rb b/activerecord/test/cases/yaml_serialization_test.rb
index bce59b4fcd..65cd54e380 100644
--- a/activerecord/test/cases/yaml_serialization_test.rb
+++ b/activerecord/test/cases/yaml_serialization_test.rb
@@ -83,4 +83,47 @@ class YamlSerializationTest < ActiveRecord::TestCase
     assert_equal 5, author.posts_count
     assert_equal 5, dumped.posts_count
   end
+
+  def test_a_yaml_version_is_provided_for_future_backwards_compat
+    coder = {}
+    Topic.first.encode_with(coder)
+
+    assert coder['active_record_yaml_version']
+  end
+
+  def test_deserializing_rails_41_yaml
+    yaml = <<-YAML.strip_heredoc
+      --- !ruby/object:Topic
+        attributes:
+          id: 
+          title: The First Topic
+          author_name: David
+          author_email_address: david@loudthinking.com
+          written_on: 2003-07-16 14:28:11.223300000 Z
+          bonus_time: 2000-01-01 14:28:00.000000000 Z
+          last_read: 2004-04-15
+          content: |
+            ---
+            :omg: :lol
+          important: 
+          approved: false
+          replies_count: 1
+          unique_replies_count: 0
+          parent_id: 
+          parent_title: 
+          type: 
+          group: 
+          created_at: 2015-03-10 17:05:42.000000000 Z
+          updated_at: 2015-03-10 17:05:42.000000000 Z
+    YAML
+    topic = YAML.load(yaml)
+
+    assert topic.new_record?
+    assert_equal nil, topic.id
+    assert_equal "The First Topic", topic.title
+    assert_equal({ omg: :lol }, topic.content)
+  end
+
+  def test_deserializing_rails_42_yaml
+  end
 end