Django自定义User模型恢复username字段，如何设置默认值为email？

步骤1：修改模型文件 #

移除User类中的username = None，保存models.py：

from django.contrib.auth.models import AbstractUser
from django.db import models
from django.utils.translation import gettext_lazy as _

class User(AbstractUser):
    # 移除原有的 username = None
    email = models.EmailField(_("Email address"), unique=True)

    USERNAME_FIELD = "email"

步骤2：生成迁移文件并退出 #

执行命令生成迁移文件：

python manage.py makemigrations

当系统提示选择修复方式时，选择选项2（退出并手动定义默认值）。

步骤3：手动修改迁移文件 #

找到刚生成的迁移文件（路径格式：[你的APP名]/migrations/000x_auto_xxxxxx_xxxx.py），替换内容如下：

from django.db import migrations, models
from django.contrib.auth import get_user_model
from django.contrib.auth.validators import UnicodeUsernameValidator

# 填充现有用户的username为对应email
def populate_username_from_email(apps, schema_editor):
    User = apps.get_model('[你的APP名]', 'User')  # 替换为实际APP名称
    for user in User.objects.all():
        if not user.username:
            user.username = user.email
            user.save(update_fields=['username'])

class Migration(migrations.Migration):
    dependencies = [
        ('[你的APP名]', '[上一个迁移文件的名称]'),  # 保留原依赖，比如0002_user_email_unique
    ]

    operations = [
        # 1. 先添加允许空值的username字段（避免迁移报错）
        migrations.AddField(
            model_name='user',
            name='username',
            field=models.CharField(
                _("username"),
                max_length=150,
                unique=True,
                null=True,
                help_text=_(
                    "Required. 150 characters or fewer. Letters, digits and @/./+/-/_ only."
                ),
                validators=[UnicodeUsernameValidator()],
                error_messages={
                    "unique": _("A user with that username already exists."),
                },
            ),
        ),
        # 2. 批量填充现有用户的username
        migrations.RunPython(populate_username_from_email),
        # 3. 修改字段为非空，恢复AbstractUser原定义
        migrations.AlterField(
            model_name='user',
            name='username',
            field=models.CharField(
                _("username"),
                max_length=150,
                unique=True,
                null=False,
                help_text=_(
                    "Required. 150 characters or fewer. Letters, digits and @/./+/-/_ only."
                ),
                validators=[UnicodeUsernameValidator()],
                error_messages={
                    "unique": _("A user with that username already exists."),
                },
            ),
        ),
    ]

注意：替换代码中的[你的APP名]和[上一个迁移文件的名称]为实际内容。

步骤4：设置新用户自动用email填充username #

因为无法直接重写AbstractUser的username字段添加默认值，用信号处理新用户创建逻辑：

1. 在APP目录下创建signals.py文件：

from django.db.models.signals import post_save
from django.dispatch import receiver
from django.contrib.auth import get_user_model

User = get_user_model()

@receiver(post_save, sender=User)
def auto_set_username(sender, instance, created, **kwargs):
    if created and not instance.username:
        instance.username = instance.email
        instance.save(update_fields=['username'])

2. 修改APP目录下的apps.py，注册信号：

from django.apps import AppConfig

class [你的APP名]Config(AppConfig):
    default_auto_field = 'django.db.models.BigAutoField'
    name = '[你的APP名]'

    def ready(self):
        import [你的APP名].signals  # 导入信号模块

步骤5：执行迁移 #

运行命令完成数据库迁移：

python manage.py migrate

内容的提问来源于stack exchange，提问作者Cool Breeze