schema.err = fmt.Errorf("invalid polymorphic type %v for %v on field %s, missing primaryKey field",
				relation.FieldSchema, schema, field.Name)
			return
		}

		// use same data type for foreign keys
		if copyableDataType(primaryKeyField.DataType) {
			relation.Polymorphic.PolymorphicID.DataType = primaryKeyField.DataType
		}
		relation.Polymorphic.PolymorphicID.GORMDataType = primaryKeyField.GORMDataType