Question

我目前正在处理一个项目，我的数据库中有四个表 - 用户，主题，问题，答案。每个用户都可以关注许多主题和问题，一个主题有很多关注者，一个问题有很多关注者和答案。此外，一个问题可能涉及多个主题。

现在我想在我关注的主题下找出所有答案，我希望按时间戳排序所有答案。我如何用flask-sqlalchemy来解决这个问题？我一整天都在上班，但找不到解决办法。

以下是代码：

class Question(db.Model):
    __tablename__ = 'questions'

    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(128), unique=True)
    body = db.Column(db.Text())
    user_id = db.Column(db.Integer, db.ForeignKey('users.id'))
    timestamp = db.Column(db.DateTime(), default=datetime.utcnow)
    followers = db.relationship('User',
                                secondary=questions_users,
                                backref=db.backref('questions_following', lazy='dynamic'),
                                lazy='dynamic')
    answers = db.relationship('Answer', backref='question', lazy='dynamic')

class User(UserMixin, db.Model):
    __tablename__ = 'users'

    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(64), unique=True)
    email = db.Column(db.String(64), unique=True)
    questions_asked = db.relationship('Question',backref='author', lazy='dynamic')
    answers = db.relationship('Answer', backref='author', lazy='dynamic')

questions_users = db.Table('questions_users',
    db.Column('question_id', db.Integer, db.ForeignKey('questions.id')),
    db.Column('follower_id', db.Integer, db.ForeignKey('users.id')))

class Topic(db.Model):
    __tablename__ = 'topics'

    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(128), unique=True)
    description = db.Column(db.Text())
    followers = db.relationship('User',
                          secondary=topics_users,
                          backref=db.backref('topics', lazy='dynamic'),
                          lazy='dynamic')
    questions = db.relationship('Question',
                            secondary=topics_questions,
                            backref=db.backref('topics', lazy='dynamic'),
                            lazy='dynamic')

class Answer(db.Model):
    __tablename__ = 'answers'

    id = db.Column(db.Integer, primary_key = True)
    body = db.Column(db.Text())
    timestamp = db.Column(db.DateTime(), default=datetime.utcnow, index=True)
    question_id = db.Column(db.Integer, db.ForeignKey('questions.id'))
    user_id = db.Column(db.Integer, db.ForeignKey('users.id'))



topics_users = db.Table('topics_users',
    db.Column('topic_id', db.Integer, db.ForeignKey('topics.id')),
    db.Column('user_id', db.Integer, db.ForeignKey('users.id')))


topics_questions = db.Table('topics_questions',
    db.Column('topic_id', db.Integer, db.ForeignKey('topics.id')),
    db.Column('question_id', db.Integer, db.ForeignKey('questions.id')))

Answer 1

如果我理解正确，那么你可以简单地join along Answer's question - topics - followers，过滤和订购：

In [7]: db.session.query(Answer).\
   ...:     join('question', 'topics', 'followers').\
   ...:     filter(User.id == 1).\
   ...:     order_by(Answer.timestamp)

由于多对多关系，结果集中可能会多次包含答案，但由于SQLAlchemy对单个实体查询进行了重复数据删除，因此这不是一个明显的问题。查询也可以使用EXISTS编写：

In [11]: db.session.query(Answer).\
    ...:     join(Question).\
    ...:     filter(Question.topics.any(
    ...:         Topic.followers.any(
    ...:             User.id == 1))).\
    ...:     order_by(Answer.timestamp)

Flask-sqlalchemy：我有4个表，如何加入它们以查找我想要的数据

1 个答案: