Question

我正在尝试使用SQLAlchemy的声明性ORM来定义如何定义一对多关系，并尝试让the example起作用，但我收到的错误是我的子类可以'找到（当然，因为它后来宣布......）

InvalidRequestError：初始化mapper Mapper | Parent | parent时，表达式'Child'找不到名称（“name'未定义'Child'）。如果这是一个类名，请考虑在定义了两个依赖类之后将此关系（）添加到类中。

但是如何在没有错误的情况下定义它？

代码：

from sqlalchemy import create_engine
from sqlalchemy import Column, Integer, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, relationship
from dev.historyMeta import VersionedMeta, VersionedListener

global engine, Base, Session
engine = create_engine('mysql+mysqldb://user:pass@localhost:3306/testdb', pool_recycle=3600)
Base = declarative_base(bind=engine, metaclass=VersionedMeta)
Session = sessionmaker(extension=VersionedListener())


class Parent(Base):
    __tablename__ = 'parent'
    id = Column(Integer, primary_key=True)
    children = relationship("Child", backref="parent")

class Child(Base):
    __tablename__ = 'child'
    id = Column(Integer, primary_key=True)
    parent_id = Column(Integer, ForeignKey('parent.id'))

Base.metadata.create_all()

Answer 1

我是这样做的：

from sqlalchemy import create_engine
from sqlalchemy import Column, Integer, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, relationship

engine = create_engine('sqlite://', echo=True)
Base = declarative_base(bind=engine)
Session = sessionmaker(bind=engine)


class Parent(Base):
    __tablename__ = 'parent'
    id = Column(Integer, primary_key=True)

class Child(Base):
    __tablename__ = 'child'
    id = Column(Integer, primary_key=True)
    parent_id = Column(Integer, ForeignKey('parent.id'))
    parent = relationship(Parent, backref='children')

Base.metadata.create_all()

SQLAlchemy声明性一对多未定义错误

1 个答案: