flask sqlalchemy 與額外字段的多對多關系

Question

我有 2 張桌子：餐廳和食物，第三張桌子 restaurant_foods 存儲兩張桌子之間的多對多關系

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)

現在，當我查詢 Restautant.query.get(1).foods 時，我希望它包含 restaurant_foods 關聯表中的 food_price 列

Answer 1

您必須使用關聯對象模式（是多對多定義的變體）：當您的關聯表包含除左右表的外鍵之外的其他列時使用它。 您不使用relationship.secondary 參數，而是將一個新類直接映射到關聯表。 關系的左側通過一對多引用關聯對象，關聯類通過多對一引用右側。 下面說明了映射到 Association 類的關聯表，其中包含一個名為 extra_data 的列，它是一個字符串值，與父子之間的每個關聯一起存儲：

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

請查看在 SQLAlchemy 中配置多對多關系。 你會想要這樣的東西：

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"
    )