Except keys of `build_record`'s argument from `create_scope` in initialize_attributes

If argument of `build_record` has key and value which is same as
default value of database, we should also except the key from
`create_scope` in `initialize_attributes`.
Because at first `build_record` initialize record object with argument
of `build_record`, then assign attributes derived from Association's scope.
In this case `record.changed` does not include the key, which value is
same as default value of database, so we should add the key to except list.

Fix #21893.

1 files changed, 6 insertions, 3 deletions

diff --git a/activerecord/lib/active_record/associations/association.rb b/activerecord/lib/active_record/associations/association.rb
index c7b396f3d4..d64ab64c99 100644
--- a/activerecord/lib/active_record/associations/association.rb
+++ b/activerecord/lib/active_record/associations/association.rb
@@ -163,9 +163,12 @@ module ActiveRecord
         @reflection = @owner.class._reflect_on_association(reflection_name)
       end
 
-      def initialize_attributes(record) #:nodoc:
+      def initialize_attributes(record, except_from_scope_attributes = nil) #:nodoc:
+        except_from_scope_attributes ||= {}
         skip_assign = [reflection.foreign_key, reflection.type].compact
-        attributes = create_scope.except(*(record.changed - skip_assign))
+        assigned_keys = record.changed
+        assigned_keys += except_from_scope_attributes.keys.map(&:to_s)
+        attributes = create_scope.except(*(assigned_keys - skip_assign))
         record.assign_attributes(attributes)
         set_inverse_instance(record)
       end
@@ -248,7 +251,7 @@ module ActiveRecord
 
         def build_record(attributes)
           reflection.build_association(attributes) do |record|
-            initialize_attributes(record)
+            initialize_attributes(record, attributes)
           end
         end