Django操作ORM小笔记

报错内容：

You are trying to add a non-nullable field 'mobile' to user without a default; we can't do that (the database needs something to popula te existing rows). Please select a fix:

1. Provide a one-off default now (will be set on all existing rows with a null value for this column)
2. Quit, and let me add a default in models.py Select an option:

models.py内容如下：

from django.db import models
from django.contrib.auth.models import AbstractUser

class User(AbstractUser):
    mobile = models.CharField(max_length=11, unique=True, verbose_name='手机号')
    class Meta:
        db_table = 'users'
        verbose_name = '用户'
        verbose_name_plural = verbose_name
    def __str__(self):
        return self.username

这个模型类继承了AbstractUser类，这个类默认提供了很多属性，比如username、first_name、email等，但是没有mobile属性。

因此这里的mobile是我们自己加的。

当新加的mobile属性这样写时：

mobile = models.CharField(max_length=11, unique=True, verbose_name='手机号')

由于没有指定该字段的默认值，即没有指定这个字段是否可以为空，所以django会有这样的提示。

解决方案：

方案①

输入1，手动指定默认值为当前时间(timezone.now为带时区的当前时间，格式：2015-07-10 14:11:19.936835+00:00)，迁移就会继续。

$ python manage.py makemigrations

You are trying to add a non-nullable field 'mobile' to user without a default; we can't do that (the database needs something to popula
te existing rows).
Please select a fix:
 1) Provide a one-off default now (will be set on all existing rows with a null value for this column)
 2) Quit, and let me add a default in models.py
Select an option: 1
Please enter the default value now, as valid Python
The datetime and django.utils.timezone modules are available, so you can do e.g. 

timezone.now

Type 'exit' to exit this prompt
>>> timezone.now
Migrations for 'user':
  easybook/apps/user/migrations/0006_user_mobile.py
    - Add field mobile to user
    
$ python manage.py migrate

方案②

输入2，退出当前对话，返回修改mobile属性的指定方式：

mobile = models.CharField(max_length=11, unique=True, null=True, verbose_name='手机号') # 增加null=True，即允许此字段为空


$ python manage.py makemigrations
Migrations for 'user':
  easybook/apps/user/migrations/0008_user_mobile.py
    - Add field mobile to user
$ python manage.py migrate