报错信息部分截取：

1File "D:\python 3.5\lib\site-packages\flask_sqlalchemy\__init__.py", line 912, in get_app
2    'No application found. Either work inside a view function or push'
3RuntimeError: No application found. Either work inside a view function or push an application context. See http://flask-sqlalchemy.pocoo.org/contexts/.

错误根源：

1class GroupForm(FlaskForm):
2    '''分组表单'''
3    menu_id = SelectField(label = "所属菜单",validators = [DataRequired("请选择菜单!")],coerce = int,
4                         choices = [(v.id,v.name) for v in Menu.query.all()],render_kw = {"class":"form-control"})
5#在form表单中执行了数据库查询操作，就会出现报错，后面发现只有在视图函数中执行数据库查询操作才不会报错(出了视图函数外的其他地方都不好使)                      

排错：

相信很多人都是这样写的init 文件的吧：

1from flask_sqlalchemy import SQLAlchemy
2from flask import Flask
3from config import Config
4db = SQLAlchemy()
5def create_app():
6    app = Flask(__name__)
7    app.config.from_object(Config)
8    Config.init_app(app)
9    db.init_app (app)
10    from .admin import admin as admin_blueprint
11    app.register_blueprint(admin_blueprint,url_prefix = '/admin')
12    return app

然后再丛manager启动文件导入create_app

1from flask_script import Manager
2from app import create_app,db
3app = create_app()
4from flask_migrate import MigrateCommand,Migrate
5manage = Manager(app)
6migrate = Migrate(app,db)
7manage.add_command('db',MigrateCommand)
8if __name__ == '__main__':
9    app.run()

这样写了之后，那么你就只能在视图函数中执行数据库操作了！！！

解决办法：

方式一 直接实例化app 不要写create_app函数了，在启动文件中直接导入app对象：

1from flask_sqlalchemy import SQLAlchemy
2from flask import Flask
3app = Flask(__name__)
4from config import Config
5app.config.from_object(Config)
6Config.init_app(app)
7db = SQLAlchemy(app)
8from .models import Auth,Role,User,Group,Menu
9
10from .admin import admin as admin_blueprint
11app.register_blueprint(admin_blueprint,url_prefix = '/admin')

方式二 如果你要你的表单中使用数据库查询，那么可以换种方式已达到同样的效果

1class GroupForm(FlaskForm):
2    '''分组表单'''
3    menu_id = SelectField(label = "所属菜单",validators = [DataRequired("请选择菜单!")],coerce = int,
4                         choices = "",render_kw = {"class":"form-control"})
5
6#然后在你的视图函数中实例化这个Form 类的时候给它赋值
7    form = MenuForm()
8    if request.method == "GET":
9        form.menu_id.choices = [(v.id,v.name) for v in Menu.query.all ()]
10
11#或者你也可以在你的Form类中写一个init方法
12class GroupForm(FlaskForm):
13    '''分组表单'''
14     menu_id = SelectField(label = "所属菜单",validators = [DataRequired("请选择菜单!")],coerce = int,
15                         choices = "",render_kw = {"class":"form-control"})
16
17     def __init__(self,*args,**kwargs):
18        super().__init__(*args,**kwargs)
19        self.menu_id.choices = [(v.id,v.name) for v in Menu.query.all()]
20        

问题解决

转自：https://blog.csdn.net/zhongqiushen/article/details/79162792