flask表单报错:"No application found. Either work inside a view function or push an application context"

flask 导入表单时报错:“RuntimeError: No application found. Either work inside a view function or push an application context.”

报错详情:

Traceback (most recent call last):
  File "F:\Projects\flask_env\lib\site-packages\sqlalchemy\util\_collections.py", line 999, in __call__
    return self.registry[key]
KeyError: 15084

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "F:/Projects/movie/manage.py", line 2, in <module>
    from utils.app import create_app
  File "F:\Projects\movie\utils\app.py", line 5, in <module>
    from app.admin.views import admin as admin_blueprint
  File "F:\Projects\movie\app\admin\views.py", line 6, in <module>
    from app.admin.forms import LoginForm, TagForm
  File "F:\Projects\movie\app\admin\forms.py", line 78, in <module>
    class MovieForm(FlaskForm):
  File "F:\Projects\movie\app\admin\forms.py", line 148, in MovieForm
    choices=[(tag.id, tag.name) for tag in Tag.query.all()],
  File "F:\Projects\flask_env\lib\site-packages\flask_sqlalchemy\__init__.py", line 514, in __get__
    return type.query_class(mapper, session=self.sa.session())
  File "F:\Projects\flask_env\lib\site-packages\sqlalchemy\orm\scoping.py", line 74, in __call__
    return self.registry()
  File "F:\Projects\flask_env\lib\site-packages\sqlalchemy\util\_collections.py", line 1001, in __call__
    return self.registry.setdefault(key, self.createfunc())
  File "F:\Projects\flask_env\lib\site-packages\sqlalchemy\orm\session.py", line 3010, in __call__
    return self.class_(**local_kw)
  File "F:\Projects\flask_env\lib\site-packages\flask_sqlalchemy\__init__.py", line 141, in __init__
    self.app = app = db.get_app()
  File "F:\Projects\flask_env\lib\site-packages\flask_sqlalchemy\__init__.py", line 912, in get_app
    'No application found. Either work inside a view function or push'
RuntimeError: No application found. Either work inside a view function or push an application context. See http://flask-sqlalchemy.pocoo.org/contexts/.

Process finished with exit code 1
form表单
class CarForm(FlaskForm):
	…… 省略号
	
	tag_label = wtforms.SelectField(
	        label='标签',
	        validators=[
	            DataRequired("选择标签")
	        ],
	        coerce=int,
	        choices=[(tag.id, tag.name) for tag in Tag.query.all()],
	        description='标签',
	        render_kw={
	            "id": "input_tag_id",
	            "class": "form-control",
	        }
	    )
	…… 省略号
视图views
@admin.route("/car/add/", methods=['GET', 'POST'])
@admin_login_required
def car_add():
    """
    添加车
    """
    form = CarForm()
    return render_template('admin/car_add.html',form=form)

报错原因:

form表单中的Tag.query.all()执行了查询语句,查询语句尽量在视图函数中完成。

解决方式:

将原代码form表单调整改为:
class CarForm(FlaskForm):
	…… 省略号
	
	tag_label = wtforms.SelectField(
	        label='标签',
	        validators=[
	            DataRequired("选择标签")
	        ],
	        coerce=int,
	        choices=“ ”,
	        description='标签',
	        render_kw={
	            "id": "input_tag_id",
	            "class": "form-control",
	        }
	    )
	…… 省略号
将原代码views视图调整改为:
@admin.route("/car/add/", methods=['GET', 'POST'])
@admin_login_required
def car_add():
    """
    添加车
    """
    form = CarForm()
    form.tag_label.choices = [(tag.id, tag.name) for tag in Tag.query.all ()]
    return render_template('admin/car_add.html',form=form)
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