Python 如何使用SQLAlchemy设置具有关联对象的邻接列表？

我正在尝试创建一个数据库模型，在这个模型中，您可以拥有一组产品，这些产品可以是其他产品的一部分，也可以包含其他产品。我已经想出了这样做的方法：

product_to_product = Table(
    "product_to_product",
    Base.metadata,
    Column("id", Integer, primary_key=True),
    Column("parent_id", Integer, ForeignKey("products.id")),
    Column("child_id", Integer, ForeignKey("products.id")),
)


class Product(Base):
    __tablename__ = "products"

    id = Column(Integer, primary_key=True)

    parents = relationship(
        "Product",
        secondary=product_to_product,
        primaryjoin=id == product_to_product.c.parent_id,
        secondaryjoin=id == product_to_product.c.child_id,
        backref="children",
    )

root = Product()

parent1 = Product()
parent2 = Product()

child1 = Product()
child2 = Product()
child3 = Product()

root.children = [parent1, parent2]
parent1.children = [child1, child2, child3]
parent2.children = [child1, child2]

class ParentReference(Base):
    __tablename__ = "parent_references"

    id = Column(Integer, primary_key=True)
    parent_id = Column(Integer, ForeignKey("products.id"))
    child_id = Column(Integer, ForeignKey("products.id"))
    additional_data = Column(String)


class Product(Base):
    __tablename__ = "products"

    id = Column(Integer, primary_key=True)

    parents = relationship(
        "Product",
        secondary=ParentReference,
        primaryjoin=id == ParentReference.child_id,
        secondaryjoin=id == ParentReference.parent_id,
        backref=backref("children"),
    )

root = Product()
parent1 = Product()
parent2 = Product()
child1 = Product()
child2 = Product()
child3 = Product()

parent1.parent_references = [
    ParentReference(parent=root, child=parent1, extra_data="Hello World!")
]
root.children.append(parent2)
parent1.children = [child1, child2, child3]
parent2.children = [child1, child2]

这让我可以添加如下产品：

product_to_product = Table(
    "product_to_product",
    Base.metadata,
    Column("id", Integer, primary_key=True),
    Column("parent_id", Integer, ForeignKey("products.id")),
    Column("child_id", Integer, ForeignKey("products.id")),
)


class Product(Base):
    __tablename__ = "products"

    id = Column(Integer, primary_key=True)

    parents = relationship(
        "Product",
        secondary=product_to_product,
        primaryjoin=id == product_to_product.c.parent_id,
        secondaryjoin=id == product_to_product.c.child_id,
        backref="children",
    )

root = Product()

parent1 = Product()
parent2 = Product()

child1 = Product()
child2 = Product()
child3 = Product()

root.children = [parent1, parent2]
parent1.children = [child1, child2, child3]
parent2.children = [child1, child2]

class ParentReference(Base):
    __tablename__ = "parent_references"

    id = Column(Integer, primary_key=True)
    parent_id = Column(Integer, ForeignKey("products.id"))
    child_id = Column(Integer, ForeignKey("products.id"))
    additional_data = Column(String)


class Product(Base):
    __tablename__ = "products"

    id = Column(Integer, primary_key=True)

    parents = relationship(
        "Product",
        secondary=ParentReference,
        primaryjoin=id == ParentReference.child_id,
        secondaryjoin=id == ParentReference.parent_id,
        backref=backref("children"),
    )

root = Product()
parent1 = Product()
parent2 = Product()
child1 = Product()
child2 = Product()
child3 = Product()

parent1.parent_references = [
    ParentReference(parent=root, child=parent1, extra_data="Hello World!")
]
root.children.append(parent2)
parent1.children = [child1, child2, child3]
parent2.children = [child1, child2]

然后，我可以抓取所有的产品，父母/孩子之间的链接完全按照我的意愿工作

现在，我想转而使用关联对象来管理链接，因为我希望有更多的数据。我尝试过这样设置：

product_to_product = Table(
    "product_to_product",
    Base.metadata,
    Column("id", Integer, primary_key=True),
    Column("parent_id", Integer, ForeignKey("products.id")),
    Column("child_id", Integer, ForeignKey("products.id")),
)


class Product(Base):
    __tablename__ = "products"

    id = Column(Integer, primary_key=True)

    parents = relationship(
        "Product",
        secondary=product_to_product,
        primaryjoin=id == product_to_product.c.parent_id,
        secondaryjoin=id == product_to_product.c.child_id,
        backref="children",
    )

root = Product()

parent1 = Product()
parent2 = Product()

child1 = Product()
child2 = Product()
child3 = Product()

root.children = [parent1, parent2]
parent1.children = [child1, child2, child3]
parent2.children = [child1, child2]

class ParentReference(Base):
    __tablename__ = "parent_references"

    id = Column(Integer, primary_key=True)
    parent_id = Column(Integer, ForeignKey("products.id"))
    child_id = Column(Integer, ForeignKey("products.id"))
    additional_data = Column(String)


class Product(Base):
    __tablename__ = "products"

    id = Column(Integer, primary_key=True)

    parents = relationship(
        "Product",
        secondary=ParentReference,
        primaryjoin=id == ParentReference.child_id,
        secondaryjoin=id == ParentReference.parent_id,
        backref=backref("children"),
    )

root = Product()
parent1 = Product()
parent2 = Product()
child1 = Product()
child2 = Product()
child3 = Product()

parent1.parent_references = [
    ParentReference(parent=root, child=parent1, extra_data="Hello World!")
]
root.children.append(parent2)
parent1.children = [child1, child2, child3]
parent2.children = [child1, child2]

我发现了许多这样做的例子，如果通过多对多关系链接在一起的对象是两个不同的对象（如

User

和

Community

），但在这种情况下，它是同一个对象。我的尝试是从不同的示例中拼凑而成的，但它与以前的脚本不兼容。我也看到过一些例子使用了

association\u proxy

函数和其他几种方法，但我无法实现这一点

---

我的目标是能够像以前一样添加产品、链接产品和导航产品，还能够从

产品

访问

ParentReference

对象，这样我就可以获取产品上的附加数据。有人能帮我解决这个问题吗？

经过更多的尝试和错误，我找到了解决方法。以下是我的解决方案：

class ParentReference(Base):
    __tablename__ = "parent_references"

    parent_id = Column(Integer, ForeignKey("products.id"), primary_key=True)
    child_id = Column(Integer, ForeignKey("products.id"), primary_key=True)
    extra_data = Column(String)

    parent = relationship(
        "Product",
        primaryjoin=lambda: ParentReference.child_id == Product.id,
        backref="child_references"
    )
    child = relationship(
        "Product",
        primaryjoin=lambda: ParentReference.parent_id == Product.id,
        backref="parent_references"
    )


class Product(Base):
    __tablename__ = "products"

    id = Column(Integer, primary_key=True)

    parents = relationship(
        "Product",
        secondary="parent_references",
        primaryjoin=lambda: Product.id == ParentReference.parent_id,
        secondaryjoin=lambda: Product.id == ParentReference.child_id,
        backref="children"
    )

其工作原理如下：

product_to_product = Table(
    "product_to_product",
    Base.metadata,
    Column("id", Integer, primary_key=True),
    Column("parent_id", Integer, ForeignKey("products.id")),
    Column("child_id", Integer, ForeignKey("products.id")),
)


class Product(Base):
    __tablename__ = "products"

    id = Column(Integer, primary_key=True)

    parents = relationship(
        "Product",
        secondary=product_to_product,
        primaryjoin=id == product_to_product.c.parent_id,
        secondaryjoin=id == product_to_product.c.child_id,
        backref="children",
    )

root = Product()

parent1 = Product()
parent2 = Product()

child1 = Product()
child2 = Product()
child3 = Product()

root.children = [parent1, parent2]
parent1.children = [child1, child2, child3]
parent2.children = [child1, child2]

class ParentReference(Base):
    __tablename__ = "parent_references"

    id = Column(Integer, primary_key=True)
    parent_id = Column(Integer, ForeignKey("products.id"))
    child_id = Column(Integer, ForeignKey("products.id"))
    additional_data = Column(String)


class Product(Base):
    __tablename__ = "products"

    id = Column(Integer, primary_key=True)

    parents = relationship(
        "Product",
        secondary=ParentReference,
        primaryjoin=id == ParentReference.child_id,
        secondaryjoin=id == ParentReference.parent_id,
        backref=backref("children"),
    )

root = Product()
parent1 = Product()
parent2 = Product()
child1 = Product()
child2 = Product()
child3 = Product()

parent1.parent_references = [
    ParentReference(parent=root, child=parent1, extra_data="Hello World!")
]
root.children.append(parent2)
parent1.children = [child1, child2, child3]
parent2.children = [child1, child2]

它允许我访问父/子对象，以及引用对象和其中的额外数据