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：

1from django.db import models
2from django.contrib.auth.models import AbstractUser
3
4class User(AbstractUser):
5    mobile = models.CharField(max_length=11, unique=True, verbose_name='手机号')
6    class Meta:
7        db_table = 'users'
8        verbose_name = '用户'
9        verbose_name_plural = verbose_name
10    def __str__(self):
11        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。

1$ python manage.py makemigrations
2
3You 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
4te existing rows).
5Please select a fix:
6 1) Provide a one-off default now (will be set on all existing rows with a null value for this column)
7 2) Quit, and let me add a default in models.py
8Select an option: 1
9Please enter the default value now, as valid Python
10The datetime and django.utils.timezone modules are available, so you can do e.g. 
11
12timezone.now
13
14Type 'exit' to exit this prompt
15>>> timezone.now
16Migrations for 'user':
17  easybook/apps/user/migrations/0006_user_mobile.py
18    - Add field mobile to user
19    
20$ 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：

1mobile = 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
2
3
4$ python manage.py makemigrations
5Migrations for 'user':
6  easybook/apps/user/migrations/0008_user_mobile.py
7    - Add field mobile to user
8$ python manage.py migrate