我是Flask Web开发的新手（还在学习）。 我试图从我的flask应用程序的注册页面注册一个新用户，然后我收到了这个错误。

"SQLite DateTime type only accepts Python "
sqlalchemy.exc.StatementError: (builtins.TypeError) SQLite DateTime type only accepts Python datetime and date objects a
s input.
[SQL: INSERT INTO user (username, email, password_hash, about_me, last_seen) VALUES (?, ?, ?, ?, ?)]
[parameters: [{'password_hash': 'pbkdf2:sha256:150000$Wknz8xPs$b1694e1d9b6b8f6a2c171147c37a1f96ff27be9da39ee825cf442f382
0c32313', 'email': '[email protected]', 'username': 'test', 'about_me': None}]]
127.0.0.1 - - [08/Jun/2019 15:07:18] "POST /register HTTP/1.1" 500 -

这是我的models.py

from datetime import datetime
from app import db
from werkzeug.security import generate_password_hash, check_password_hash
from flask_login import UserMixin
from hashlib import md5
from app import login

@login.user_loader
def load_user(id):
    return User.query.get(int(id))

class User(UserMixin ,db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(64), index=True, unique=True)
    email = db.Column(db.String(120), index=True, unique=True)
    password_hash = db.Column(db.String(128))
    posts = db.relationship('Post', backref='author', lazy='dynamic')
    about_me = db.Column(db.String(140))
    last_seen = db.Column(db.DateTime, default="datetime.utcnow")

    def __repr__(self):
        return '<User {}>'.format(self.username)

    def set_password(self, password):
        self.password_hash = generate_password_hash(password)

    def check_password(self, password):
        return check_password_hash(self.password_hash, password)

    def avatar(self, size):
        digest = md5(self.email.lower().encode('utf-8')).hexdigest()
        return 'https://www.gravatar.com/avatar/{}?d=identicon&s={}'.format(
        digest, size)

这是我的注册视图function

@app.route('/register', methods=['GET', 'POST'])
def register():
    if current_user.is_authenticated:
        return redirect(url_for('index'))
    form = RegistrationForm()
    if form.validate_on_submit():
        user = User(username=form.username.data, email=form.email.data)
        user.set_password(form.password.data)
        db.session.add(user)
        db.session.commit()
        flash('Congratulations, you are now a registered user!')
        return redirect(url_for('login'))
    return render_template('register.html', title='Register', form=form)
分析解答

您正在尝试将function传递给default参数。如文档所示，这应该是function引用（但不是调用）。在您的示例中，您提供了string。

更改：

last_seen = db.Column(db.DateTime, default="datetime.utcnow")

至：

last_seen = db.Column(db.DateTime, default=datetime.utcnow)

这就是Mega Tutorial让你做from datetime import datetime的原因。

附注：对于SQLite，此错误消息实际上不正确。 SQLite不强制执行严格的列类型，因此您可以将字符串插入整数类型列等。这并不是说错误没有用，因为SQLAlchemy无论如何都将依赖于列数据类型，但SQLite本身并没有严格执行，可能会在以后抓住你 off-guard 。

import sqlite3

with sqlite3.connect(':memory:') as conn:
    c = conn.cursor()

    # Create a table and try enforce a datetime type
    c.execute("""
              CREATE TABLE IF NOT EXISTS test(
                 id PRIMARY KEY,
                 datetime DATETIME)
              """)

    conn.commit()

    c.execute("""
              INSERT INTO test
              VALUES (?, ?)
              """, (None, '123')) # Insert non-datetime value into datetime col
    conn.commit()

    c.execute("SELECT * FROM test")

    print(c.fetchall()) # Worked just fine