Pony ORM实体单向映射报错

Question

我有2张桌子。表A & 表B

TableA

+------+----------------+-----------+
|  id  | some_attribute | tableB_id |
+------+----------------+-----------+

id=主键

some_attribute=varchar

TableB_id=外键

TableB

+------+----------------+
|  id  | some_attribute |
+------+----------------+

id=主键

some_attribute=varchar

我的代码：

# establish a connection with the database (MySQL)
db = Connection.Connection.connect_db_server_default()


class TableB(db.Entity):
    _table_ = "table_b"
    id = PrimaryKey(int, auto=False)
    some_attribute = Required(str)


class TableA(db.Entity):
    _table_ = "table_a"
    id = PrimaryKey(int, auto=False)
    some_attribute = Required(str)
    TableB_id = Set(TableA)

Gives the following error:
pony.orm.core.ERDiagramError: Reverse attribute for TableA.TableB_id not found

我的问题：

如何使用 Pony ORM 重新创建上述关系？实体是否总是需要双向关系？

有什么方法可以实现适当的数据库规范化，还是我必须使用一些不同的 ORM 模块？

Answer 1

看起来这里的错误是我自己的，Pony-ORM 文档中指定了这个问题的答案。

我假设由于 TableB 是独立的并且是被引用的 table，它不应该有任何类型的从自身到 TableA 的映射。然而，documentation 指定：

Some mappers (e.g. Django) require defining relationships on one side only. Pony requires defining relationships on both sides explicitly (as The Zen of Python reads: Explicit is better than implicit), which allows the user to see all relationships from the perspective of each entity.

以及在文档同一部分发布的示例：

# If we want to allow an instance of OrderItem to exist without
# being assigned to an 'Order', we can define the order attribute as Optional:
class Order(db.Entity):
    items = Set(lambda: Order)

class OrderItem(db.Entity):
    order = Optional(Order)

即使Pony-ORM works is completely wrong in terms of database normalization方式，也无法以其他方式发挥作用。不应该先花一些时间正确阅读文档，就不要盲目使用模块。

道德课

NE假设。 R阅读您的 D文档。

Pony ORM实体单向映射报错

Pony ORM Entity Unidirectional Mapping gives an error

python

mysql

orm

database-normalization

ponyorm

我的代码：

我的问题：

道德课