Define id_was to get the previous value of the primary key

Currently when we call id_was and we have a custom primary key name
Active Record will return the current value of the primary key. This
make impossible to correctly do an update operation if you change the
id.

Fixes #16413

1 files changed, 7 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/attribute_methods/primary_key.rb b/activerecord/lib/active_record/attribute_methods/primary_key.rb
index cadad60ddd..9bd333bbac 100644
--- a/activerecord/lib/active_record/attribute_methods/primary_key.rb
+++ b/activerecord/lib/active_record/attribute_methods/primary_key.rb
@@ -39,6 +39,12 @@ module ActiveRecord
         read_attribute_before_type_cast(self.class.primary_key)
       end
 
+      # Returns the primary key previous value.
+      def id_was
+        sync_with_transaction_state
+        attribute_was(self.class.primary_key)
+      end
+
       protected
 
       def attribute_method?(attr_name)
@@ -54,7 +60,7 @@ module ActiveRecord
           end
         end
 
-        ID_ATTRIBUTE_METHODS = %w(id id= id? id_before_type_cast).to_set
+        ID_ATTRIBUTE_METHODS = %w(id id= id? id_before_type_cast id_was).to_set
 
         def dangerous_attribute_method?(method_name)
           super && !ID_ATTRIBUTE_METHODS.include?(method_name)