SQLAlchemy - 自引用表错误答案

【问题标题】：SQLAlchemy - Error with self-referring tableSQLAlchemy - 自引用表错误
【发布时间】：2019-05-05 07:52:12
【问题描述】：

我正在尝试构建一个系统，用户可以在其中回复其他帖子的帖子，但是当我尝试运行该程序时出现错误：

sqlalchemy.exc.InvalidRequestError:
    One or more mappers failed to initialize - can't proceed with initialization of other mappers.
    Triggering mapper: 'Mapper|Post|post'.
    Original exception was: 'Table' object has no attribute 'id'

这是我的代码：

class Post(db.Model):
    id = db.Column(db.Integer, primary_key=True, default=pidgen.gen(8))
    title = db.Column(db.String(500))
    body = db.Column(db.String(10000))
    timestamp = db.Column(db.DateTime, index=True, default=datetime.utcnow)
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'))
    children = db.relationship('Post', backref='parent', lazy='dynamic')
    group_id = db.Column(db.Integer, db.ForeignKey('group.id'))
    parent_id = db.Column(db.Integer, db.ForeignKey('post.id'))
    def __repr__(self):
        return '<Post {}>'.format(self.body)

【问题讨论】：

标签： python sql sqlalchemy flask-sqlalchemy

【解决方案1】：

您的代码对我有用。还有什么你不包括的吗？您如何执行数据库创建？

这是我运行它的方式。我不得不添加自己的用户和组，并删除了 pidgen.get()，因为我不清楚它们的来源。

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from datetime import datetime
import pytz

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////tmp/test.db'
db = SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    def __repr__(self):
        return '<User %r>' % self.username

class Group(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(80), unique=True, nullable=False)
    def __repr__(self):
        return '<Group %r>' % self.name

class Post(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(500))
    body = db.Column(db.String(10000))
    timestamp = db.Column(db.DateTime, index=True, default=datetime.utcnow)
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'))
    children = db.relationship('Post', backref='parent', lazy='dynamic')
    group_id = db.Column(db.Integer, db.ForeignKey('group.id'))
    parent_id = db.Column(db.Integer, db.ForeignKey('post.id'))
    def __repr__(self):
        return '<Post {}>'.format(self.body)

db.create_all()

运行：

python testapp.py

给我这个

sqlite> .schema post
CREATE TABLE post (
    id INTEGER NOT NULL, 
    title VARCHAR(500), 
    body VARCHAR(10000), 
    timestamp DATETIME, 
    user_id INTEGER, 
    group_id INTEGER, 
    parent_id INTEGER, 
    PRIMARY KEY (id), 
    FOREIGN KEY(user_id) REFERENCES user (id), 
    FOREIGN KEY(group_id) REFERENCES "group" (id), 
    FOREIGN KEY(parent_id) REFERENCES post (id)
);
CREATE INDEX ix_post_timestamp ON post (timestamp);

【讨论】：