django 在原有表格添加或删除字段的实例_Python

django 在原有表格添加或删除字段的实例

2021-02-25 00:53JackLiu16 Python

今天小编就为大家分享一篇django 在原有表格添加或删除字段的实例，具有很好的参考价值，希望对大家有所帮助。一起跟随小编过来看看吧

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：

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									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>