flask_sqlalchemy RuntimeError: Working outside of application context. 报错解决

---

在使用flask_sqlalchemy删表、建表时出现报错：

Traceback (most recent call last):
  File "xxx\test.py", line 40, in <module>
    db.drop_all()
  File "xxx\Python\Python38\lib\site-packages\flask_sqlalchemy\extension.py", line 901, in drop_all
    self._call_for_binds(bind_key, "drop_all")
  File "xxx\Python\Python38\lib\site-packages\flask_sqlalchemy\extension.py", line 855, in _call_for_binds
    engine = self.engines[key]
  File "xxx\Python\Python38\lib\site-packages\flask_sqlalchemy\extension.py", line 636, in engines
    app = current_app._get_current_object()  # type: ignore[attr-defined]
  File "xxx\Python\Python38\lib\site-packages\werkzeug\local.py", line 513, in _get_current_object
    raise RuntimeError(unbound_message) from None
RuntimeError: Working outside of application context.

This typically means that you attempted to use functionality that needed
the current application. To solve this, set up an application context
with app.app_context(). See the documentation for more information.

源代码如下（代码借鉴于站内另一大佬文章）：
运行环境软件包版本：flask_sqlalchemy:3.0.3，flask：2.2.3：

# -*- coding: UTF-8 -*-
from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://root:[email protected]:3306/test'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.config['SQLALCHEMY_ECHO'] = True

# 创建组件对象
db = SQLAlchemy(app)
# 构建模型类  类->表  类属性->字段  实例对象->记录
class User(db.Model):
    __tablename__ = 't_user'  # 设置表名, 表名默认为类名小写
    id = db.Column(db.Integer, primary_key=True)  # 设置主键, 默认自增
    name = db.Column('username', db.String(20), unique=True)  # 设置字段名 和 唯一约束
    age = db.Column(db.Integer, default=10, index=True)  # 设置默认值约束 和 索引
    
    
if __name__ == '__main__':
    db.drop_all()
    db.create_all()
    app.run(debug=True)

---

运行代码时出现文章开头错误，网上查询解决方法未果。重新阅读报错信息，发现信息最后一行To solve this, set up an application context with app.app_context()。于是找到app.app_context()源码，部分如下：

def app_context(self) -> AppContext:
    """Create an :class:`~flask.ctx.AppContext`. Use as a ``with``
    block to push the context, which will make :data:`current_app`
    point at this application.

    An application context is automatically pushed by
    :meth:`RequestContext.push() <flask.ctx.RequestContext.push>`
    when handling a request, and when running a CLI command. Use
    this to manually create a context outside of these situations.

    ::

        with app.app_context():
            init_db()

发现使用方法为：

with app.app_context():
    init_db() # 这个地方替换为自己需要运行的函数/方法

---

于是将源码更改为：

# -*- coding: UTF-8 -*-
from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://root:[email protected]:3306/test'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.config['SQLALCHEMY_ECHO'] = True

# 创建组件对象
db = SQLAlchemy(app)
# 构建模型类  类->表  类属性->字段  实例对象->记录
class User(db.Model):
    __tablename__ = 't_user'  # 设置表名, 表名默认为类名小写
    id = db.Column(db.Integer, primary_key=True)  # 设置主键, 默认自增
    name = db.Column('username', db.String(20), unique=True)  # 设置字段名 和 唯一约束
    age = db.Column(db.Integer, default=10, index=True)  # 设置默认值约束 和 索引
    
    
if __name__ == '__main__':
    with app.app_context():
        # 删除所有继承自db.Model的表
        db.drop_all()
        # 创建所有继承自db.Model的表
        db.create_all()
    app.run(debug=True)

运行程序后，成功建表

2023-03-10 09:47:41,843 INFO sqlalchemy.engine.Engine 
CREATE TABLE t_user (
        id INTEGER NOT NULL AUTO_INCREMENT, 
        username VARCHAR(20), 
        age INTEGER, 
        PRIMARY KEY (id), 
        UNIQUE (username)
)

数据库内也建表成功，问题解决