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django 在原有表格添加或删除字段的实例

2018年08月21日  | 移动技术网IT编程  | 我要评论

香港公厕门事件,gts除皱,bzmh

一、如果models.py文件为时:

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

会提示:

(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

输入:1 (这里要求你设置新建字段的默认值,它会在新建这个字段的同时把默认值也添加上去,)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()
>>>

这里面不好修改

可以

(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')
 

二、如果models.py文件为时:

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)

blank

设置为true时,字段可以为空。设置为false时,字段是必须填写的。字符型字段charfield和textfield是用空字符串来存储空值的。如果为true,字段允许为空,默认不允许.

null

设置为true时,django用null来存储空值。日期型、时间型和数字型字段不接受空字符串。所以设置integerfield,datetimefield型字段可以为空时,需要将blank,null均设为true。如果为true,空值将会被存储为null,默认为false。如果想设置booleanfield为空时可以选用nullbooleanfield型字段。

(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)

三、数据库设计是整个网站开发的核心

补充: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
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>

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