如何修复Django注册时UNIQUE constraint failed: auth_user.username错误

问题描述 #

尝试使用Django邮件模块在用户注册时给新用户发送欢迎邮件，但遇到错误：

UNIQUE constraint failed: auth_user.username

以下是相关代码：

views.py #

from django.shortcuts import render, redirect
from django.contrib.auth import login
from django.contrib.auth.decorators import login_required
from . import forms

# Create your views here.
def home(request):
    return render(request,'home.html')

@login_required
def customer_page(request):
    return render(request,'home.html')

@login_required
def courier_page(request):
    return render(request,'home.html')

def sign_up(request):
    form = forms.SignUPForm()
    if request.method=='POST':
        form=forms.SignUPForm(request.POST)
        
        if form.is_valid():
            email=form.cleaned_data.get('email').lower()
            
            user= form.save(commit=False)
            user.useranme = email  # 此处存在拼写错误
            user.save() 
            
            login(request,user,backend='django.contrib.auth.backends.ModelBackend')
            return redirect('/')
                    
    return render(request,'sign_up.html',{
        'form':form
    })

signals.py #

# my signals.py file
from email.base64mime import body_decode
from django.db.models.signals import post_save
from django.dispatch import receiver
from django.core.mail import send_mail
from django.conf import settings
from django.contrib.auth.models import User
from django.template.loader import render_to_string
from django.core import mail
connection = mail.get_connection()

@receiver(post_save,sender=User)
def send_welcome_email(sender,instance,created,**kwarg):
    if created and instance.email:
        connection.open()
        body=render_to_string(
            'welcome_email_template.html',
            {
                'name':instance.get_full_name()
            }
        )
        email2 = mail.EmailMessage(
    'Welcome to fast Parcle',
     body,
    settings.DEFAULT_FROM_EMAIL,
    [instance.email],
    fail_silently=False,
)
        connection.send_messages([email2])
        connection.close() 

settings.py #

#also my settings.py

from pathlib import Path


# Build paths inside the project like this: BASE_DIR / 'subdir'.
BASE_DIR = Path(__file__).resolve().parent.parent


# Quick-start development settings - unsuitable for production
# See https://docs.djangoproject.com/en/3.1/howto/deployment/checklist/

# SECURITY WARNING: keep the secret key used in production secret!
SECRET_KEY = ''

# SECURITY WARNING: don't run with debug turned on in production!
DEBUG = True

ALLOWED_HOSTS = []


# Application definition

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    
    'bootstrap4',
    'social_django',
    'core.apps.CoreConfig',
]

MIDDLEWARE = [
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
]

ROOT_URLCONF = 'fastparcel.urls'

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [],
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
                'social_django.context_processors.backends',
                'social_django.context_processors.login_redirect',
            ],
        },
    },
]

WSGI_APPLICATION = 'fastparcel.wsgi.application'


# Database
# https://docs.djangoproject.com/en/3.1/ref/settings/#databases

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': BASE_DIR / 'db.sqlite3',
    }
}


# Password validation
# https://docs.djangoproject.com/en/3.1/ref/settings/#auth-password-validators

AUTH_PASSWORD_VALIDATORS = [
    {
        'NAME': 'django.contrib.auth.password_validation.UserAttributeSimilarityValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.MinimumLengthValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.CommonPasswordValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.NumericPasswordValidator',
    },
]


# Internationalization
# https://docs.djangoproject.com/en/3.1/topics/i18n/

LANGUAGE_CODE = 'en-us'

TIME_ZONE = 'UTC'

USE_I18N = True

USE_L10N = True

USE_TZ = True


# Static files (CSS, JavaScript, Images)
# https://docs.djangoproject.com/en/3.1/howto/static-files/

STATIC_URL = '/static/'
LOGIN_URL='/sign_in/'
LOGIN_REDRICTED_URL='/'  # 此处拼写错误，应为LOGIN_REDIRECT_URL
AUTHENTICATION_BACKENDS = (
    'social_core.backends.facebook.FacebookOAuth2',
    'django.contrib.auth.backends.ModelBackend',
)

SOCIAL_AUTH_FACEBOOK_KEY="######"
SOCIAL_AUTH_FACEBOOK_SECRET="############"
SOCIAL_AUTH_FACEBOOK_SCOPE=['email']
SOCIAL_AUTH_FACEBOOK_PROFILE_EXTRA_PARAMS= {
    'fields':'id,name,email'
}

SECURE_SSL_REDIRECT = False
EMAIL_BACKEND = 'django.core.mail.backends.smtp.EmailBackend'
EMAIL_HOST='smtp.gmail.com'
EMAIL_USE_TLS=True
EMAIL_PORT=587
EMAIL_HOST_USER='####'
EMAIL_HOST_PASSWORD='####'
DEFAULT_FROM_EMAIL='FAST Parcle <no_reply@fastparcle.localhost>'
ACCOUNT_SIGNUP_FORM_CLASS = 'core.forms.SignupForm'

错误原因分析 #

1. 核心拼写错误：views.py中user.useranme = email是笔误，正确字段名应为username。这导致邮箱未被赋值给正确的字段，表单提交的原始username值未被覆盖，若该值已存在于数据库中，就会触发唯一约束冲突。
2. 其他潜在问题：
   • settings.py中LOGIN_REDRICTED_URL拼写错误，会导致登录后跳转异常。
   • signals.py中全局创建邮件连接，可能引发连接复用状态异常。

解决方案 #

1. 修复views.py中的拼写错误 #

将user.useranme = email修改为：

user.username = email

确保用户名被设置为唯一的邮箱地址，避免重复值引发约束错误。

2. 优化signals.py的邮件发送逻辑 #

将全局邮件连接改为函数内创建，使用上下文管理器自动管理连接生命周期：

from django.db.models.signals import post_save
from django.dispatch import receiver
from django.conf import settings
from django.contrib.auth.models import User
from django.template.loader import render_to_string
from django.core import mail

@receiver(post_save, sender=User)
def send_welcome_email(sender, instance, created, **kwargs):
    if created and instance.email:
        # 上下文管理器自动处理连接的打开和关闭
        with mail.get_connection() as connection:
            # 处理用户无全名的情况， fallback到用户名
            user_name = instance.get_full_name() or instance.username
            body = render_to_string(
                'welcome_email_template.html',
                {'name': user_name}
            )
            email = mail.EmailMessage(
                '欢迎加入Fast Parcel',
                body,
                settings.DEFAULT_FROM_EMAIL,
                [instance.email],
                connection=connection,
                fail_silently=False,
            )
            email.send()

3. 修复settings.py中的拼写错误 #

将LOGIN_REDRICTED_URL='/'修改为：

LOGIN_REDIRECT_URL='/'

4. 优化注册表单避免重复问题 #

如果你的SignUPForm继承自UserCreationForm，建议隐藏username字段，直接用邮箱作为用户名：

# forms.py示例
from django.contrib.auth.forms import UserCreationForm
from django.contrib.auth.models import User

class SignUPForm(UserCreationForm):
    class Meta:
        model = User
        fields = ('email', 'password1', 'password2')
    
    def save(self, commit=True):
        user = super().save(commit=False)
        user.username = self.cleaned_data['email'].lower()
        if commit:
            user.save()
        return user

这样用户注册时无需输入用户名，直接用唯一的邮箱作为标识，彻底避免username重复问题。

内容的提问来源于stack exchange，提问作者mick