与表之间的关系冲突

Question

我一直在控制台上收到警告，我读了这么多书快要发疯了，但我一直无法解决这个问题：

SAWarning: relationship 'Book.users' will copy column user.uid to column user_book.uid, which conflicts with relationship(s): 'User.books' (copies user.uid to user_book.uid). If this is not intention, consider if these relationships should be linked with back_populates, or if viewonly=True should be applied to one or more if they are read-only. For the less common case that foreign key constraints are partially overlapping, the orm.foreign() annotation can be used to isolate the columns that should be written towards. The 'overlaps' parameter may be used to remove this warning.

控制台在本通知中引用的表格如下：

user_book = db.Table('user_book',
                     db.Column('uid', db.Integer, db.ForeignKey('user.uid'), primary_key=True),
                     db.Column('bid', db.Text, db.ForeignKey('book.bid'), primary_key=True),
                     db.Column('date_added', db.DateTime(timezone=True), server_default=db.func.now())
                     )


class User(db.Model):
    __tablename__ = 'user'

    uid = db.Column(db.Integer, primary_key=True)
    email = db.Column(db.String(25), nullable=False)
    hash = db.Column(db.String(), nullable=False)
    first_name = db.Column(db.String(30), nullable=True)
    last_name = db.Column(db.String(80), nullable=True)
    books = db.relationship('Book', secondary=user_book)

class Book(db.Model):
    __tablename__ = 'book'

    bid = db.Column(db.Text, primary_key=True)
    title = db.Column(db.Text, nullable=False)
    authors = db.Column(db.Text, nullable=False)
    thumbnail = db.Column(db.Text, nullable=True)
    users = db.relationship('User', secondary=user_book)

我使用 user_book table 向用户显示他添加的书籍。

我错过了什么？我借此机会问一下，表和外键之间的语义关系是否正确？

Answer 1

如警告消息所示，您的关系中缺少 back_populates= 属性：

class User(db.Model):
# …
    books = db.relationship('Book', secondary=user_book, back_populates="users")
# …
    
class Book(db.Model):
# …
    users = db.relationship('User', secondary=user_book, back_populates="books")
# …

与表之间的关系冲突

Conflicts with relationship between tables

python

postgresql

sqlalchemy