【sqlalchemy】自定义映射表的元类

sqlalchemy自定义映射表的元类有两种方式：函数declarative_base和as_declarative装饰器

• 通过继承DeclarativeMeta元类，在使用declarative_base函数时传递给metaclass参数

from sqlalchemy import Column, Integer, Text, create_engine
from sqlalchemy.ext.declarative import declarative_base, DeclarativeMeta

class BaseTableMetaclass(DeclarativeMeta):

    def __init__(cls, classname: str, bases, dict_, **kw: object) -> None:
        # 自动生成表名的设置
        setattr(cls, "__tablename__", classname.lower())
        # 添加通用的表字段
        setattr(cls, "id", Column(Integer, primary_key=True, autoincrement=True))
        super(BaseTableMetaclass, cls).__init__(classname, bases, dict_, **kw)


Base = declarative_base(metaclass=BaseTableMetaclass)


class TbTest(Base):
    status = Column(Integer)
    note = Column(Text)

• 定义一个类并使用as_declarative装饰器，使之成为表映射类的元类

以下是官方文档的示例：

from sqlalchemy.ext.declarative import as_declarative

@as_declarative()
class Base(object):
    @declared_attr
    def __tablename__(cls):
        return cls.__name__.lower()
    id = Column(Integer, primary_key=True)

class MyMappedClass(Base):
    # ...

对比两种方式，as_declarative装饰器的方式更加直观，代码易读性会高一些