两个表之间的关系，SQLAlchemy

Question

我想在 AuthorComments 和 Reply to his comments 之间建立关系。

这是我的models.py:

class AuthorComments(Base):

    id = db.Column(db.Integer, primary_key=True)
    author_id = db.Column(db.Integer, db.ForeignKey('author.id'))
    name = db.Column(db.String(50))
    email = db.Column(db.String(50), unique=True)
    comment = db.Column(db.Text)
    live = db.Column(db.Boolean)

    comments = db.relationship('Reply', backref='reply', lazy='joined')

    def __init__(self,author, name, email, comment, live=True):

        self.author_id = author.id
        self.name = name
        self.email = email
        self.comment = comment
        self.live = live

class Reply(Base):

    id = db.Column(db.Integer, primary_key=True)
    reply_id = db.Column(db.Integer, db.ForeignKey('author.id'))
    name = db.Column(db.String(50))
    email = db.Column(db.String(50), unique=True)
    comment = db.Column(db.Text)
    live = db.Column(db.Boolean)

    def __init__(self,author, name, email, comment, live=True):

        self.reply_id = author.id
        self.name = name
        self.email = email
        self.comment = comment
        self.live = live

为什么我会收到此错误： sqlalchemy.exc.InvalidRequestError

InvalidRequestError: One or more mappers failed to initialize - can't proceed with initialization of other mappers. Original exception was: Could not determine join condition between parent/child tables on relationship AuthorComments.comments - there are no foreign keys linking these tables. Ensure that referencing columns are associated with a ForeignKey or ForeignKeyConstraint, or specify a 'primaryjoin' expression.

Answer 1

你的问题是 SQLAlchemy 不知道，对于给定的子行 table (Reply)，父行 table (AuthorComments) 到 select！您需要在 Reply 中定义一个 foreign-key 列，该列引用其父项 AuthorComments.

的列

Here 是关于在 SQLAlchemy 中定义一对多关系的文档。

像这样：

class AuthorComments(Base):
    __tablename__ = 'author_comment'
    ...

class Reply(Base):
    ...
    author_comment_id = db.Column(db.Integer, db.ForeignKey('author_comment.id'))
    ...
    author_comment = db.relationship(
        'AuthorComments',
        backref='replies',
        lazy='joined'
        )

将导致每个 reply 获得与 author_comment 的关系，这样 some_reply.author_comment_id == some_author_comment.id 或 None 如果不存在这样的等式。

backref 允许每个 author_comment 与一个名为 replies 的回复集合相互关联，满足上述条件。

两个表之间的关系，SQLAlchemy

Relationship between two tables, SQLAlchemy

python

rdbms

sqlalchemy

flask-sqlalchemy