Flask sqlalchemy 与额外字段的多对多关系

Question

我有 2 张桌子：餐厅和食物，第三张桌子 restaurant_foods 存储两张桌子之间的多对多关系

restaurants_foods = db.Table('restaurants_foods',
    db.Column('restaurant_id', db.Integer, db.ForeignKey('restaurants.id'), primary_key=True),
    db.Column('food_id', db.Integer, db.ForeignKey('foods.id'), primary_key=True),
    db.Column('food_price', db.Float)
)

class Food(Model):
    __tablename__ = "foods"

    id = db.Column(db.Integer, primary_key=True, autoincrement=True)    
    name = db.Column(db.String(255), nullable=False)
    description = db.Column(db.String(255), nullable=True)


class Restaurant(Model):
    __tablename__ = "restaurants"

    id = db.Column(db.Integer, primary_key=True, autoincrement=True)    
    name = db.Column(db.String(255), nullable=False)
    foods = db.relationship('Food', secondary=restaurants_foods)

现在，当我查询 Restautant.query.get(1).foods 时，我希望它包含 restaurant_foods 关联表中的 food_price 列

Answer 1

您必须使用关联对象模式（是多对多定义的变体）：当您的关联表包含除左右表的外键之外的其他列时使用它。您不使用relationship.secondary 参数，而是将一个新类直接映射到关联表。关系的左侧通过一对多引用关联对象，关联类通过多对一引用右侧。下面说明了映射到 Association 类的关联表，其中包含一个名为 extra_data 的列，它是一个字符串值，与父子之间的每个关联一起存储：

class Association(Base):
    __tablename__ = 'association'
    left_id = Column(Integer, ForeignKey('left.id'), primary_key=True)
    right_id = Column(Integer, ForeignKey('right.id'), primary_key=True)
    extra_data = Column(String(50))
    child = relationship("Child", back_populates="parents")
    parent = relationship("Parent", back_populates="children")

class Parent(Base):
    __tablename__ = 'left'
    id = Column(Integer, primary_key=True)
    children = relationship("Association", back_populates="parent")

class Child(Base):
    __tablename__ = 'right'
    id = Column(Integer, primary_key=True)
    parents = relationship("Association", back_populates="child")

Answer 2

请查看在 SQLAlchemy 中配置多对多关系。你会想要这样的东西：

restaurants_foods = db.Table('restaurants_foods',
    db.Column('restaurant_id', db.Integer, db.ForeignKey('restaurants.id'), primary_key=True),
    db.Column('food_id', db.Integer, db.ForeignKey('foods.id'), primary_key=True),
    db.Column('food_price', db.Float))


class Food(Model):
    __tablename__ = "foods"

    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    name = db.Column(db.String(255), nullable=False)
    description = db.Column(db.String(255), nullable=True)
    restaurants = relationship(
        "Restaurant",
        secondary=restaurant_foods,
        back_populates="foods"
    )


class Restaurant(Model):
    __tablename__ = "restaurants"

    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    name = db.Column(db.String(255), nullable=False)
    foods = relationship(
        "Food",
        secondary=restaurant_foods,
        back_populates="restaurants"
    )