使用flask_sqlalchemy的多对多查询

Question

I got this models in a SQLAlchemy based app

class Task(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(512))
    status = db.Column(db.Enum(Status))


class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(512))
    user_tasks = db.relationship('Task',
                                 secondary=user_tasks, lazy='subquery',
                                 backref=db.backref('users', lazy=True)
                                )

user_tasks = db.Table('user_tasks',
    db.Column('task_id', db.Integer, db.ForeignKey('task.id'), primary_key=True),
    db.Column('user_id', db.Integer, db.ForeignKey('user.id'), primary_key=True),
    db.Column('value', db.Integer)
)

I want to join the 3 tables (using flask_sqlalchemy rather than a raw query) equivalent to:

db.session.execute(
                    'SELECT u.id, u.name, ut.value\
                     FROM user u\
                     JOIN user_tasks ut\
                     ON u.id = ut.user_id\
                     AND ut.task_id = :task_id\
                     JOIN task t\
                     ON t.id = ut.task_id',
                     {'task_id': task_id}
                   )

Thanks in advance

Answer 1

Below is a tested example.
Please note that due to the different ways these tables could be joined you will need to explicitly specify the joins, as in the example below, in order for SQLAlchemy to perform the query.

db.session.query(User.id,User.name,user_tasks.c.value).\ 
    join(user_tasks,user_tasks.c.user_id==User.id).\ 
    filter(user_tasks.task_id==task_id).\
    join(Task,Task.id==user_tasks.c.task_id).all()