Correctly detect mutation on serialized columns mapping to binary

Fixes #16701

3 files changed, 31 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/type/binary.rb b/activerecord/lib/active_record/type/binary.rb
index d29ff4e494..005a48ef0d 100644
--- a/activerecord/lib/active_record/type/binary.rb
+++ b/activerecord/lib/active_record/type/binary.rb
@@ -22,6 +22,11 @@ module ActiveRecord
         Data.new(super)
       end
 
+      def changed_in_place?(raw_old_value, value)
+        old_value = type_cast_from_database(raw_old_value)
+        old_value != value
+      end
+
       class Data # :nodoc:
         def initialize(value)
           @value = value.to_s
@@ -30,10 +35,15 @@ module ActiveRecord
         def to_s
           @value
         end
+        alias_method :to_str, :to_s
 
         def hex
           @value.unpack('H*')[0]
         end
+
+        def ==(other)
+          other == to_s || super
+        end
       end
     end
   end
diff --git a/activerecord/lib/active_record/type/serialized.rb b/activerecord/lib/active_record/type/serialized.rb
index abeea769c4..5b512433b0 100644
--- a/activerecord/lib/active_record/type/serialized.rb
+++ b/activerecord/lib/active_record/type/serialized.rb
@@ -26,6 +26,11 @@ module ActiveRecord
         end
       end
 
+      def changed_in_place?(raw_old_value, value)
+        return false if value.nil?
+        subtype.changed_in_place?(raw_old_value, coder.dump(value))
+      end
+
       def accessor
         ActiveRecord::Store::IndifferentHashAccessor
       end
diff --git a/activerecord/test/cases/dirty_test.rb b/activerecord/test/cases/dirty_test.rb
index 0c77eedb52..5cb6b97117 100644
--- a/activerecord/test/cases/dirty_test.rb
+++ b/activerecord/test/cases/dirty_test.rb
@@ -682,6 +682,22 @@ class DirtyTest < ActiveRecord::TestCase
     assert_not pirate.changed?
   end
 
+  test "in place mutation for binary" do
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = :binaries
+      serialize :data
+    end
+
+    klass.create!(data: "foo")
+    binary = klass.first
+
+    assert_not binary.changed?
+
+    binary.data << "bar"
+
+    assert binary.changed?
+  end
+
   private
     def with_partial_writes(klass, on = true)
       old = klass.partial_writes?