python - Flask - 我无法从flask_app导入用户模型

Question

当我尝试在flask_app(包含应用程序)中导入“User”模型时，出现错误，出现 ImportError: Cannot import name 'User' from 'models' 错误。

forms.py - 我正在尝试从flask_app导入用户

from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField, SubmitField, BooleanField
from wtforms.validators import DataRequired, Length, Email, EqualTo, ValidationError
from flask_app import User


class RegistrationForm(FlaskForm):
    username = StringField('Username',
                           validators=[DataRequired(), Length(min=2, max=20)])
    email = StringField('Email',
                        validators=[DataRequired(), Email()])
    password = PasswordField('Password', validators=[DataRequired()])
    confirm_password = PasswordField('Confirm Password',
                                     validators=[DataRequired(), EqualTo('password')])
    submit = SubmitField('Sign Up')

    def validate_username(self, username):
        user = User.query.filter_by(username=username.data).first()
        if user:
            raise ValidationError('That username is taken. Please choose a different one.')

    def validate_email(self, email):
        user = User.query.filter_by(email=email.data).first()
        if user:
            raise ValidationError('That email is taken. Please choose a different one.')

这是用户模型:

from datetime import datetime
from flask import Flask, render_template, url_for, flash, redirect
from flask_sqlalchemy import SQLAlchemy
from forms import RegistrationForm, LoginForm
from flask_bcrypt import Bcrypt
from flask_login import login_user, current_user, logout_user, login_required, LoginManager

app = Flask(__name__)
app.config['SECRET_KEY'] = ''
app.config['SQLALCHEMY_DATABASE_URI'] = ''
db = SQLAlchemy(app)
bcrypt = Bcrypt(app)
login_manager = LoginManager(app)
login_manager.login_view = 'login'
login_manager.login_message_category = 'info'


class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(20), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)
    image_file = db.Column(db.String(20), nullable=False, default='default.jpg')
    password = db.Column(db.String(60), nullable=False)
    posts = db.relationship('Post', backref='author', lazy=True)

    def __repr__(self):
        return f"User('{self.username}', '{self.email}', '{self.image_file}')"


@app.route("/")
@app.route("/home")
def home():
    return render_template('home.html', posts=posts)


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

给了我这个:

2020-01-12 08:58:53,282: Error running WSGI application
2020-01-12 08:58:53,284: ImportError: cannot import name 'User' from 'models' (/home/kickie/mysite/models.py)
2020-01-12 08:58:53,287:   File "/var/www/fdfdfd_pythonanywhere_com_wsgi.py", line 16, in <module>
2020-01-12 08:58:53,289:     from flask_app import app as application  # noqa
2020-01-12 08:58:53,290: 
2020-01-12 08:58:53,291:   File "/home/kickie/mysite/flask_app.py", line 4, in <module>
2020-01-12 08:58:53,292:     from forms import RegistrationForm, LoginForm
2020-01-12 08:58:53,292: 
2020-01-12 08:58:53,293:   File "/home/kickie/mysite/forms.py", line 4, in <module>
2020-01-12 08:58:53,293:     from flask_app import User

我收到错误是因为应用程序在这里？我应该将用户移动到另一个位置吗？

Answer 1

发生这种情况是因为您正在执行循环导入

# inside flask_app.py
from forms import RegistrationForm

和

# inside forms.py
from flask_app import User

Check this explanation

<小时/>

简单的解决方案

如果您决定采用此结构，请避免代码中出现此问题

1) 只需从 forms.py 中删除 fromflask_app import User

2) 将其导入到使用模型的方法中。

from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField, SubmitField, BooleanField
from wtforms.validators import DataRequired, Length, Email, EqualTo, ValidationError
# REMOVE THE IMPORT


class RegistrationForm(FlaskForm):
    username = StringField('Username',
                           validators=[DataRequired(), Length(min=2, max=20)])
    email = StringField('Email',
                        validators=[DataRequired(), Email()])
    password = PasswordField('Password', validators=[DataRequired()])
    confirm_password = PasswordField('Confirm Password',
                                     validators=[DataRequired(), EqualTo('password')])
    submit = SubmitField('Sign Up')

    def validate_username(self, username):
        # Import them inside the methods that are using the Model
        from flask_app import User
        user = User.query.filter_by(username=username.data).first()
        if user:
            raise ValidationError('That username is taken. Please choose a different one.')

    def validate_email(self, email):
        # Import them inside the methods that are using the Model
        from flask_app import User
        user = User.query.filter_by(email=email.data).first()
        if user:
            raise ValidationError('That email is taken. Please choose a different one.')