Flask DateTime won't set with default datetime.utcnow

问题:

I am new to SQLAlchemy and have been unable to set the DateTime for created. I have tried using the "default" option found in many examples. I have also tried setting it manually (I have it commented out). Neither have worked so far. Any help would be appreciated.

models.py  import datetime from flask.ext.sqlalchemy import SQLAlchemy from werkzeug import generate_password_hash, check_password_hash  db = SQLAlchemy()  class User(db.Model):    __tablename__    = 'users'   uid              = db.Column(db.Integer, primary_key=True)   firstname        = db.Column(db.String(40))   lastname         = db.Column(db.String(40))   email            = db.Column(db.String(120), unique=True)   created          = db.Column(db.DateTime, default=datetime.datetime.utcnow())   confirmed        = db.Column(db.DateTime, nullable=True)   pwdhash          = db.Column(db.String(100))    def __init__(self, firstname, lastname, email, password):     self.firstname = firstname.title()     self.lastname  = lastname.title()     self.email     = email.lower()     self.set_password(password)     #self.created   = datetime.datetime.utcnow()     self.confirmed = None    def set_password(self, password):     self.pwdhash   = generate_password_hash(password)    def check_password(self, password):     return check_password_hash(self.pwdhash, password)  routes.py  from tasks import app from datetime import datetime from flask import render_template, request, flash, session, url_for, redirect from forms import ContactForm, SignupForm, SigninForm from flask.ext.mail import Message, Mail from models import db, User, Tags, Tasks  @app.route('/signup', methods=['GET', 'POST']) def signup():   form = SignupForm()    if 'email' in session:     return redirect(url_for('profile'))     if request.method == 'POST':     if form.validate() == False:       return render_template('signup.html', form=form)     else:       newuser = User(form.firstname.data, form.lastname.data, form.email.data, form.password.data)       db.session.add(newuser)       db.session.commit()        session['email'] = newuser.email       return redirect(url_for('profile'))    elif request.method == 'GET':     return render_template('signup.html', form=form) 

回答1:

The problem with your default is that you're calling datetime.utcnow immediately there, and the value returned (at the time of class definition) is always used as default. You need to pass the callable itself like following:

# Note the lack of parenthesis after datetime.utcnow created = db.Column(db.DateTime, default=datetime.datetime.utcnow) 

This way SQLAlchemy will call datetime.utcnow itself upon row insert.

回答2:

This is a also good solution :

  created = db.Column(db.DateTime, server_default=db.func.now())   updated = db.Column(db.DateTime, server_default=db.func.now(), server_onupdate=db.func.now()) 

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