Question

我想设计一个具有用户和项目的应用程序，用户可以是项目的候选者，并且可以选择作为项目的参与者。所以我使用下面的代码：

class User(db.Model):
    __tablename__ = 'users'
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(64), unique=True)


class Participate(db.Model):
    __tablename__ = 'participates'
    project_id = db.Column(db.Integer, db.ForeignKey('projects.id'),
                           primary_key=True)
    candidate_id = db.Column(db.Integer, db.ForeignKey('users.id'),
                             primary_key=True)
    participant_id = db.Column(db.Integer, db.ForeignKey('users.id'),
                               primary_key=True)
    candidate_timestamp = db.Column(db.DateTime, default=datetime.utcnow)
    participate_timestamp = db.Column(db.DateTime, default=datetime.utcnow)


class Project(db.Model):
    __tablename__ = 'projects'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(64), unique=True)

    candidates = db.relationship('Participate',
                                 foreign_keys=[Participate.candidate_id],
                                 backref=db.backref('candidate_projects', lazy='joined'),
                                 lazy='dynamic')
    participants = db.relationship('Participate',
                                   foreign_keys=[Participate.participant_id],
                                   backref=db.backref('participate_projects', lazy='joined'),
                                   lazy='dynamic')

然后我尝试在shell中创建一些数据：

# python manage.py shell
>>> db
<SQLAlchemy engine='mysql://connection_uri?charset=utf8&use_unicode=0'>
>>> Project
<class 'app.models_.Project'>
>>> User
<class 'app.models_.User'>
>>> Participate
<class 'app.models_.Participate'>
>>> jerry = User(username='jerry')

我遇到了这个例外：

NoForeignKeysError: Could not determine join condition between parent/child     
tables on relationship Project.candidates - there are no foreign keys linking 
these tables.  Ensure that referencing columns are associated with a ForeignKey 
or ForeignKeyConstraint, or specify a 'primaryjoin' expression.

我是sqlalchemy的新手，设计数据库的正确方法是什么？

Answer 1

candidate_id和participant_id属性是用户外键。您正在与Project表建立关系。您需要将它们移动到User表，然后它们才能正常工作。

然后，如果您需要获得项目的所有候选人或参与者，您可以使用这些关系并按您感兴趣的项目过滤它们。

在flask-sqlalchemy中的关联表

1 个答案: