Question

我是python的新手（不到一天！）。我正在尝试使用Flask构建Restful API。我有class TaskModel(db.Model):类，它与任务具有自引用关系。实际上，一个任务可以有很多前任（dependsOn字段）。

但是当我在下面添加关系时，出现此错误： sqlalchemy.exc.NoForeignKeysError: Could not determine join condition between parent/child tables on relationship TaskModel.dependsOn - there are no foreign keys linking these tables.

我的整个Task类别如下：

class TaskModel(db.Model):
    """
    Task Model
    """

    # table name
    __tablename__ = 'tasks'

    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(128), nullable=False)
    department = db.Column(db.String(128), nullable=False)
    earliestStart = db.Column(db.String(10), nullable=False)
    latestEnd = db.Column(db.String(10), nullable=False)
    duration = db.Column(db.String(10), nullable=False)
    dnetworkId = db.Column(db.Integer, db.ForeignKey('dnetworks.id'), nullable=False)
    dependsOn = db.relationship('TaskModel', backref='tasks',remote_side=[id], lazy=True)


....

class TaskSchema(Schema):
    """
    Task Schema
    """
    id = fields.Int(dump_only=True)
    name = fields.Str(required=True)
    department = fields.Str(required=True)
    earliestStart = fields.Str(required=True)
    latestEnd = fields.Str(required=True)
    dnetworkId = fields.Int(required=True)
    duration = fields.Str(required=True)
    dependsOn = fields.Nested('self', many=True, exclude=('dependsOn',))
    # dependsOn = fields.Nested('self', exclude=('dependsOn',), default=None, many=True)

先谢谢您了:)

Answer 1

在用于关系的SqlAlchemy中，您应该定义两种方式，以下是您可能寻找的完整工作示例：

import os
from sqlalchemy.orm import relationship, backref
from flask import Flask
from flask_sqlalchemy import SQLAlchemy

BASE_DIR = os.path.dirname(os.path.abspath(__file__))
app = Flask(__name__)
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////{}/my.db'.format(BASE_DIR)

db = SQLAlchemy(app)


class TaskModel(db.Model):
    __tablename__ = 'tasks'

    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(128), nullable=True)
    parent_id =  db.Column(db.Integer, db.ForeignKey("tasks.id"))
    children = relationship("TaskModel",
        backref=backref('parent', remote_side=[id])
    )


if __name__ == "__main__":
    db.create_all()
    tm = TaskModel(name='Test1')
    db.session.add(tm)
    db.session.commit()

注意parent_id和childs，两者的组合将为您提供所需的信息，与任务之间的自相关性，在数据库上将parent_id添加到表中。

一对多自引用关系SQLAlchemy

1 个答案: