code: def field_definition_post_save(sender, instance, created, raw, **kwargs):
      
      model_class = instance.model_def.model_class().render_state()
      field = instance.construct_for_migrate()
      field.model = model_class
      if created:
          if hasattr(instance._state, '_creation_default_value'):
              field.default = instance._state._creation_default_value
              delattr(instance._state, '_creation_default_value')
          add_column = popattr(instance._state, '_add_column', True)
          if add_column:
              perform_ddl('add_field', model_class, field)
              # If the field definition is raw we must re-create the model class
              # since ModelDefinitionAttribute.save won't be called
              if raw:
                  instance.model_def.model_class().mark_as_obsolete()
      else:
          old_field = instance._state._pre_save_field
          delattr(instance._state, '_pre_save_field')
          perform_ddl('alter_field', model_class, old_field, field, strict=True)
docs: This signal is connected by all FieldDefinition subclasses
      see comment in FieldDefinitionBase for more details