django 在原有表格添加或删除字段的实例

timestamp = models.DateTimeField('保存日期')

(env8) D:\Desktop\env8\Scripts\mysite>python manage.py makemigrations
You are trying to add a non-nullable field 'timestamp' to article without a defa
ult; we can't do that (the database needs something to populate existing rows).
Please select a fix:
 1) Provide a one-off default now (will be set on all existing rows)
 2) Quit, and let me add a default in models.py

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()
>>>

(env8) D:\Desktop\env8\Scripts\mysite>python manage.py shell
(env8) D:\Desktop\env8\Scripts\mysite>from django.db import connection
(env8) D:\Desktop\env8\Scripts\mysite>cursor=connection.cursor()
(env8) D:\Desktop\env8\Scripts\mysite>cursor.execute('ALTER TABLEArticle add column timestamp varchar(100) default 0')
 

timestamp = models.DateTimeField('保存日期',default=timezone.now,blank=False, null=False)
timestamp = models.DateTimeField('保存日期',default=timezone.now,blank=True, null=True)

(env8) D:\Desktop\env8\Scripts\mysite>python manage.py makemigrations就不会有下面的提示
(env8) D:\Desktop\env8\Scripts\mysite>python manage.py migrate 就行了中间不会设置数据类型（很容易出错）（若要设置默认值）

(env8) D:\Desktop\env8\Scripts\mysite>python manage.py makemigrations
You are trying to add a non-nullable field 'timestamp' to article without a defa
ult; we can't do that (the database needs something to populate existing rows).
Please select a fix:
 1) Provide a one-off default now (will be set on all existing rows)
 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()
>>> '2017-12-16 05:04:31.000'（添加字段的数据类型格式）
Migrations for 'blog':
 0002_article_timestamp.py:
  - Add field timestamp to article
(env8) D:\Desktop\env8\Scripts\mysite>python manage.py migrate
Operations to perform:
 Synchronize unmigrated apps: staticfiles, ckeditor_uploader, messages, ckedito
r, bootstrap3
 Apply all migrations: admin, blog, contenttypes, auth, sessions
Synchronizing apps without migrations:
 Creating tables...
  Running deferred SQL...
 Installing custom SQL...
Running migrations:
 Rendering model states... DONE
 Applying blog.0002_article_timestamp...D:Desktop\env8\lib\site-packa
ges\django\db\models\fields\__init__.py:1474: RuntimeWarning: DateTimeField Arti
cle.timestamp received a naive datetime (2017-12-16 05:04:31) while time zone su
pport is active.
 RuntimeWarning)
 OK
(env8) D:\Desktop\env8\Scripts\mysite>