1 files changed, 10 insertions, 2 deletions
diff --git a/activerecord/lib/active_record/attribute_set.rb b/activerecord/lib/active_record/attribute_set.rb
index 66fcaf6945..9142317646 100644
--- a/activerecord/lib/active_record/attribute_set.rb
+++ b/activerecord/lib/active_record/attribute_set.rb
@@ -10,6 +10,10 @@ module ActiveRecord
       attributes[name] || Attribute.null(name)
     end
 
+    def []=(name, value)
+      attributes[name] = value
+    end
+
     def values_before_type_cast
       attributes.transform_values(&:value_before_type_cast)
     end
@@ -24,7 +28,7 @@ module ActiveRecord
     end
 
     def keys
-      attributes.initialized_keys
+      attributes.each_key.select { |name| self[name].initialized? }
     end
 
     def fetch_value(name)
@@ -49,7 +53,7 @@ module ActiveRecord
     end
 
     def initialize_dup(_)
-      @attributes = attributes.dup
+      @attributes = attributes.deep_dup
       super
     end
 
@@ -64,6 +68,10 @@ module ActiveRecord
       end
     end
 
+    def accessed
+      attributes.select { |_, attr| attr.has_been_read? }.keys
+    end
+
     protected
 
     attr_reader :attributes