python - Flask-SQLAlchemy:sqlite3 IntegrityError

Question

我正在创建一个应用程序来替换浏览器中的当前选项卡管理器。我在组 - 表主题和选项卡 - 表选项卡之间创建了一个简单的一对多关系。如果我删除它，我希望能够自动删除主题的 child 。这是我目前拥有的:

from flask import request, redirect, url_for, render_template, Flask
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import exc
from flask_whooshee import Whooshee
from datetime import datetime

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///database.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False

db = SQLAlchemy(app)
whooshee = Whooshee(app)

@whooshee.register_model('topic_name')
class Topic(db.Model):
    __tablename__ = 'topic'
    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    topic_name = db.Column(db.String, unique=True, nullable=False)
    topic_created = db.Column(db.DateTime, default=datetime.utcnow)
    topic_changed = db.Column(db.DateTime, default=datetime.utcnow)
    topic_tabs = db.relationship('Tab', backref='topic', cascade='all, delete-orphan', lazy='dynamic')

@whooshee.register_model('tab_name', 'tab_link', 'tab_description')
class Tab(db.Model):
    __tablename__ = 'tab'
    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    tab_name = db.Column(db.String, nullable=False)
    tab_link = db.Column(db.String, unique=True, nullable=False)
    tab_favicon = db.Column(db.String)
    tab_description = db.Column(db.String)
    tab_created = db.Column(db.DateTime, default=datetime.utcnow)
    tab_changed = db.Column(db.DateTime, default=datetime.utcnow)
    topic_id = db.Column(db.Integer, db.ForeignKey('topic.id'))

@app.route('/', methods=['GET'])
def index():
    return "Test"

if __name__ == '__main__':
    db.create_all()
    try:
        db.session.commit()
    except exc.IntegrityError as e:
        print(str(e))
        db.session.rollback()

    top = Topic(topic_name='Test')
    db.session.add(top)
    try:
        db.session.commit()
    except exc.IntegrityError as e:
        print(str(e))
        db.session.rollback()

    top2 = Topic(topic_name='Test2')
    db.session.add(top2)
    try:
        db.session.commit()
    except exc.IntegrityError as e:
        print(str(e))
        db.session.rollback()

    t1 = Tab(tab_name='t1', tab_link='t1l', tab_favicon='t1f', tab_description='t1d', topic_id=top.id)
    t2 = Tab(tab_name='t2', tab_link='t2l', tab_favicon='t2f', tab_description='t2d', topic_id=top.id)
    t3 = Tab(tab_name='t3', tab_link='t3l', tab_favicon='t3f', tab_description='t3d', topic_id=top.id)

    db.session.add(t1)
    db.session.add(t2)
    db.session.add(t3)
    try:
        db.session.commit()
    except exc.IntegrityError as e:
        print(str(e))
        db.session.rollback()
    import uuid
    app.secret_key = str(uuid.uuid4())
    app.run(debug=True)

问题是当我尝试在数据库中添加某些内容时出现完整性错误，但我不确定会出现什么问题。如果我停止服务器，我还想将以前的记录保存在数据库中，我该如何实现？
UPD :即使我完全删除我的数据库，也会发生以下行为。简单运行脚本后，我收到此错误 python script_name.py在一个空文件夹中。
UPD2 : 如果有人需要检查数据库是否存在，有一个特殊的辅助函数 https://sqlalchemy-utils.readthedocs.io/en/latest/database_helpers.html#database-exists

(sqlite3.IntegrityError) UNIQUE constraint failed: topic.topic_name [SQL: 'INSERT INTO topic (topic_name, topic_created, topic_changed) VALUES (?, ?, ?)'] [parameters: ('Test', '2018-09-03 05:21:08.728564', '2018-09-03 05:21:08.728564')] (Background on this error at: http://sqlalche.me/e/gkpj)

(sqlite3.IntegrityError) UNIQUE constraint failed: topic.topic_name [SQL: 'INSERT INTO topic (topic_name, topic_created, topic_changed) VALUES (?, ?, ?)'] [parameters: ('Test2', '2018-09-03 05:21:08.730562', '2018-09-03 05:21:08.730562')] (Background on this error at: http://sqlalche.me/e/gkpj)

(sqlite3.IntegrityError) UNIQUE constraint failed: tab.tab_link [SQL: 'INSERT INTO tab (tab_name, tab_link, tab_favicon, tab_description, tab_created, tab_changed, topic_id) VALUES (?, ?, ?, ?, ?, ?, ?)'] [parameters: ('t1', 't1l', 't1f', 't1d', '2018-09-03 05:21:08.733561', '2018-09-03 05:21:08.733561', None)] (Background on this error at: http://sqlalche.me/e/gkpj)

Answer 1

您的脚本是 WSGI 应用程序，因此运行为 __main__ .如果您使用 debug=True作为 app.run() 的参数服务器将启动，设置 Debug模式:打开并重新启动 with stat ，执行 __name__ == '__main__'再次阻止(每次更改脚本并在服务器运行时保存它时再次阻止)。

当您在一个空的/已删除的数据库上启动您的应用程序时，第一次 __name__ == '__main__'块被执行，它创建数据库并插入两个 Topic和三个 Tab您在该块中创建的对象。然后它设置 Debug模式并重新启动，再次执行该块，尝试第二次插入这五个对象。

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello_world():
    return "Hello, World!"

if __name__ == '__main__':
    print(__name__)
    app.run(debug=True)

输出:

__main__ # <-- fist time around it creates DB and objects
 * Serving Flask app "main" (lazy loading)
 * Environment: production
   WARNING: Do not use the development server in a production environment.
   Use a production WSGI server instead.
 * Debug mode: on
 * Restarting with stat # <-- re-executing your script
__main__ # <-- trying to create the same objects again, violating the UNIQUE constraint
 * Debugger is active!
 * Debugger PIN: 302-544-855
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)