python - 如何让 Mypy 识别不可为 null 的 ORM 属性？

Question

Mypy 将 ORM 不可空实例属性推断为可选。

文件名:test.py

from sqlalchemy.orm import decl_api, registry
from sqlalchemy import BigInteger, Column, String

mapper_registry = registry()


class Base(metaclass=decl_api.DeclarativeMeta):
    __abstract__ = True

    registry = mapper_registry
    metadata = mapper_registry.metadata

    __init__ = mapper_registry.constructor


class Person(Base):
    __tablename__ = "persons"

    id = Column(BigInteger, primary_key=True, autoincrement=True)
    name = Column(String(40), nullable=False)


def main(person: Person):
    person_id = person.id
    person_name = person.name

    reveal_locals()

运行 mypy test.py 产生:

test.py:27: note: Revealed local types are:
test.py:27: note:     person: test.Person
test.py:27: note:     person_id: Union[builtins.int, None]
test.py:27: note:     person_name: Union[builtins.str, None]

据我所知，person_id 和 person_name 应该分别是 int 和 str，因为它们被设置为不可为空。

我在这里错过了什么？

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相关图书馆:

SQLAlchemy         1.4.25
sqlalchemy2-stubs  0.0.2a15
mypy               0.910
mypy-extensions    0.4.3

Answer 1

我在使用 mypy 评估 nullable=False 列时遇到了同样的问题。我的一位队友在 SqlAlchemy 文档中找到了答案:

https://docs.sqlalchemy.org/en/14/orm/extensions/mypy.html#introspection-of-columns-based-on-typeengine

The types are by default always considered to be Optional, even forthe primary key and non-nullable column. The reason is because whilethe database columns “id” and “name” can’t be NULL, the Pythonattributes id and name most certainly can be None without an explicitconstructor:

他们在那篇文章中还列出了缓解措施，将列显式声明为映射类型。