Report the attribute on ActiveRecord::SerializationTypeMismatch

activerecord/lib/active_record/attribute_methods/serialization.rb

@@ -54,7 +54,7 @@ def serialize(attr_name, class_name_or_coder = Object)
           elsif [:load, :dump].all? { |x| class_name_or_coder.respond_to?(x) }
             class_name_or_coder
           else
-            Coders::YAMLColumn.new(class_name_or_coder)
+            Coders::YAMLColumn.new(attr_name, class_name_or_coder)
           end
 
           decorate_attribute_type(attr_name, :serialize) do |type|

activerecord/lib/active_record/coders/yaml_column.rb

@@ -5,7 +5,8 @@ module Coders # :nodoc:
     class YAMLColumn # :nodoc:
       attr_accessor :object_class
 
-      def initialize(object_class = Object)
+      def initialize(attr_name, object_class = Object)
+        @attr_name = attr_name
         @object_class = object_class
         check_arity_of_constructor
       end
@@ -31,7 +32,7 @@ def load(yaml)
       def assert_valid_value(obj)
         unless obj.nil? || obj.is_a?(object_class)
           raise SerializationTypeMismatch,
-            "Attribute was supposed to be a #{object_class}, but was a #{obj.class}. -- #{obj.inspect}"
+            "Attribute `#{@attr_name}` was supposed to be a #{object_class}, but was a #{obj.class}. -- #{obj.inspect}"
         end
       end
 

activerecord/lib/active_record/store.rb

@@ -78,7 +78,7 @@ class << self
 
     module ClassMethods
       def store(store_attribute, options = {})
-        serialize store_attribute, IndifferentCoder.new(options[:coder])
+        serialize store_attribute, IndifferentCoder.new(store_attribute, options[:coder])
         store_accessor(store_attribute, options[:accessors]) if options.has_key? :accessors
       end
 
@@ -177,12 +177,12 @@ def self.prepare(object, store_attribute)
       end
 
       class IndifferentCoder # :nodoc:
-        def initialize(coder_or_class_name)
+        def initialize(attr_name, coder_or_class_name)
           @coder =
             if coder_or_class_name.respond_to?(:load) && coder_or_class_name.respond_to?(:dump)
               coder_or_class_name
             else
-              ActiveRecord::Coders::YAMLColumn.new(coder_or_class_name || Object)
+              ActiveRecord::Coders::YAMLColumn.new(attr_name, coder_or_class_name || Object)
             end
         end
 

activerecord/test/cases/coders/yaml_column_test.rb

@@ -5,46 +5,48 @@ module ActiveRecord
   module Coders
     class YAMLColumnTest < ActiveRecord::TestCase
       def test_initialize_takes_class
-        coder = YAMLColumn.new(Object)
+        coder = YAMLColumn.new("attr_name", Object)
         assert_equal Object, coder.object_class
       end
 
       def test_type_mismatch_on_different_classes_on_dump
-        coder = YAMLColumn.new(Array)
-        assert_raises(SerializationTypeMismatch) do
+        coder = YAMLColumn.new("attr_name", Array)
+        error = assert_raises(SerializationTypeMismatch) do
           coder.dump("a")
         end
+        assert_equal %{Attribute `attr_name` was supposed to be a Array, but was a String. -- "a"}, error.to_s
       end
 
       def test_type_mismatch_on_different_classes
-        coder = YAMLColumn.new(Array)
-        assert_raises(SerializationTypeMismatch) do
+        coder = YAMLColumn.new("attr_name", Array)
+        error = assert_raises(SerializationTypeMismatch) do
           coder.load "--- foo"
         end
+        assert_equal %{Attribute `attr_name` was supposed to be a Array, but was a String. -- "foo"}, error.to_s
       end
 
       def test_nil_is_ok
-        coder = YAMLColumn.new
+        coder = YAMLColumn.new("attr_name")
         assert_nil coder.load "--- "
       end
 
       def test_returns_new_with_different_class
-        coder = YAMLColumn.new SerializationTypeMismatch
+        coder = YAMLColumn.new("attr_name", SerializationTypeMismatch)
         assert_equal SerializationTypeMismatch, coder.load("--- ").class
       end
 
       def test_returns_string_unless_starts_with_dash
-        coder = YAMLColumn.new
+        coder = YAMLColumn.new("attr_name")
         assert_equal "foo", coder.load("foo")
       end
 
       def test_load_handles_other_classes
-        coder = YAMLColumn.new
+        coder = YAMLColumn.new("attr_name")
         assert_equal [], coder.load([])
       end
 
       def test_load_doesnt_swallow_yaml_exceptions
-        coder = YAMLColumn.new
+        coder = YAMLColumn.new("attr_name")
         bad_yaml = "--- {"
         assert_raises(Psych::SyntaxError) do
           coder.load(bad_yaml)
@@ -52,7 +54,7 @@ def test_load_doesnt_swallow_yaml_exceptions
       end
 
       def test_load_doesnt_handle_undefined_class_or_module
-        coder = YAMLColumn.new
+        coder = YAMLColumn.new("attr_name")
         missing_class_yaml = '--- !ruby/object:DoesNotExistAndShouldntEver {}\n'
         assert_raises(ArgumentError) do
           coder.load(missing_class_yaml)

activerecord/test/cases/serialized_attribute_test.rb

@@ -240,6 +240,20 @@ def test_regression_serialized_default_on_text_column_with_null_false
     assert_equal [], light.long_state
   end
 
+  def test_unexpected_serialized_type
+    Topic.serialize :content, Hash
+    topic = Topic.create!(content: { zomg: true })
+
+    Topic.serialize :content, Array
+
+    topic.reload
+    error = assert_raise(ActiveRecord::SerializationTypeMismatch) do
+      topic.content
+    end
+    expected = "Attribute `content` was supposed to be a Array, but was a Hash. -- {:zomg=>true}"
+    assert_equal expected, error.to_s
+  end
+
   def test_serialized_column_should_unserialize_after_update_column
     t = Topic.create(content: "first")
     assert_equal("first", t.content)