docs: def _meta_schema_factory(self, columns, model, class_mixin):
          """
              Creates ModelSchema marshmallow-sqlalchemy
  
          :param columns: a list of columns to mix
          :param model: Model
          :param class_mixin: a marshamallow Schema to mix
          :return: ModelSchema
          """
          _model = model
          if columns:
              class MetaSchema(ModelSchema, class_mixin):
                  class Meta:
                      model = _model
                      fields = columns
                      strict = True
                      sqla_session = self.datamodel.session
          else:
              class MetaSchema(ModelSchema, class_mixin):
                  class Meta:
                      model = _model
                      strict = True
                      sqla_session = self.datamodel.session
          return MetaSchema