SQL 炼金关系未链接类

Question

我有两个类:

class Country(Base):
    __tablename__ = 'country'
    country_id = Column(BigInteger, primary_key=True)
    cities = relationship('city',back_populates='country')
class City(Base):
    __tablename__='city'
    country_id = Column(BigInteger,ForeignKey('country.country_id'))
    country = relationship("country",back_populates='cities')

    city_id = Column(BigInteger,primary_key=True) 
    x=Column(BigInteger)
    y=Column(BigInteger)

现在，当我创建国家/地区对象时：

c1 = City(x=0,y=0)
c2 = City(x=5,y=2)
country = Country(cities = [c1,c2])

并致电

print(c1.country_id)

None

我该如何解决这个问题？谢谢！

Answer 1

下面的脚本有效。问题中有两个变化

更改关系以匹配文档中的基本 one-to-many relationship
将实例添加到会话并刷新以从数据库中获取 ID
将主键从 BigInteger 更改为 Integer

在 SQLite 上需要将主键的类型从 BigInteger 更改为 Integer，但在 MariaDB (MySQL) 或 Postgresql 上则不需要。

import sqlalchemy as sa
from sqlalchemy import orm

Base = orm.declarative_base()


class Country(Base):
    __tablename__ = "country"
    country_id = sa.Column(sa.Integer, primary_key=True)
    cities = orm.relationship("City")


class City(Base):
    __tablename__ = "city"
    country_id = sa.Column(sa.Integer, sa.ForeignKey("country.country_id"))

    city_id = sa.Column(sa.Integer, primary_key=True)
    x = sa.Column(sa.Integer)
    y = sa.Column(sa.Integer)


engine = sa.create_engine("sqlite://", echo=True)

Base.metadata.create_all(engine)
session = orm.Session(engine)


c1 = City(x=0, y=0)
c2 = City(x=5, y=2)
country = Country(cities=[c1, c2])
session.add(country)
session.flush()


print(c1.country_id)

SQL 炼金关系未链接 类

SQL Alchemy Relationship not linking classes

sqlalchemy

SQL 炼金关系未链接类