Merge pull request #36907 from wjessop/string_attribute_should_compare_with_typecast_symbol_after_update

Serialize symbols to strings in ImmutableString serialize method

activemodel/lib/active_model/type/immutable_string.rb

@@ -9,7 +9,7 @@ module ActiveModel
 
       def serialize(value)
         case value
-        when ::Numeric, ActiveSupport::Duration then value.to_s
+        when ::Numeric, ::Symbol, ActiveSupport::Duration then value.to_s
         when true then "t"
         when false then "f"
         else super

activerecord/test/cases/dirty_test.rb

@@ -326,6 +326,13 @@ class DirtyTest < ActiveRecord::TestCase
     assert_not_predicate topic, :approved_changed?
   end
 
+  def test_string_attribute_should_compare_with_typecast_symbol_after_update
+    pirate = Pirate.create!(catchphrase: :foo)
+    pirate.update_column :catchphrase, :foo
+    pirate.catchphrase
+    assert_not_predicate pirate, :catchphrase_changed?
+  end
+
   def test_partial_update
     pirate = Pirate.new(catchphrase: "foo")
     old_updated_on = 1.hour.ago.beginning_of_day