3 files changed, 83 insertions, 0 deletions
diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index c80bce2849..5afb97803e 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -81,6 +81,10 @@ module ActiveRecord
     autoload :Validations
   end
 
+  module Coders
+    autoload :YAMLColumn, 'active_record/coders/yaml_column'
+  end
+
   module AttributeMethods
     extend ActiveSupport::Autoload
 
diff --git a/activerecord/lib/active_record/coders/yaml_column.rb b/activerecord/lib/active_record/coders/yaml_column.rb
new file mode 100644
index 0000000000..9b0df119ef
--- /dev/null
+++ b/activerecord/lib/active_record/coders/yaml_column.rb
@@ -0,0 +1,34 @@
+module ActiveRecord
+  # :stopdoc:
+  module Coders
+    class YAMLColumn
+      RESCUE_ERRORS = [ ArgumentError ]
+
+      if defined?(Psych) && defined?(Psych::SyntaxError)
+        RESCUE_ERRORS << Psych::SyntaxError
+      end
+
+      attr_accessor :object_class
+
+      def initialize(object_class = Object)
+        @object_class = object_class
+      end
+
+      def load(yaml)
+        return yaml unless yaml.is_a?(String) && yaml =~ /^---/
+        begin
+          obj = YAML::load(yaml)
+
+          unless obj.is_a?(object_class) || obj.nil?
+            raise SerializationTypeMismatch,
+              "Attribute was supposed to be a #{object_class}, but was a #{obj.class}"
+          end
+
+        rescue *RESCUE_ERRORS
+          yaml
+        end
+      end
+    end
+  end
+  # :startdoc
+end
diff --git a/activerecord/test/cases/coders/yaml_column_test.rb b/activerecord/test/cases/coders/yaml_column_test.rb
new file mode 100644
index 0000000000..f85f11b57f
--- /dev/null
+++ b/activerecord/test/cases/coders/yaml_column_test.rb
@@ -0,0 +1,45 @@
+require "cases/helper"
+
+module ActiveRecord
+  module Coders
+    class YAMLColumnTest < ActiveRecord::TestCase
+      def test_initialize_takes_class
+        coder = YAMLColumn.new(Object)
+        assert_equal Object, coder.object_class
+      end
+
+      def test_type_mismatch_on_different_classes
+        coder = YAMLColumn.new(Array)
+        assert_raises(SerializationTypeMismatch) do
+          coder.load "--- foo"
+        end
+      end
+
+      def test_nil_is_ok
+        coder = YAMLColumn.new
+        assert_nil coder.load "--- "
+      end
+
+      def test_nil_is_ok_with_different_class
+        coder = YAMLColumn.new SerializationTypeMismatch
+        assert_nil coder.load "--- "
+      end
+
+      def test_returns_string_unless_starts_with_dash
+        coder = YAMLColumn.new
+        assert_equal 'foo', coder.load("foo")
+      end
+
+      def test_load_handles_other_classes
+        coder = YAMLColumn.new
+        assert_equal [], coder.load([])
+      end
+
+      def test_load_swallows_yaml_exceptions
+        coder = YAMLColumn.new
+        bad_yaml = '--- {'
+        assert_equal bad_yaml, coder.load(bad_yaml)
+      end
+    end
+  end
+end