django 在原有表格添加或刪除字段的實例

更新時間：2018年05月27日 15:50:25 作者：JackLiu16

今天小編就為大家分享一篇django 在原有表格添加或刪除字段的實例，具有很好的參考價值，希望對大家有所幫助。一起跟隨小編過來看看吧

一、如果models.py文件為時：

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

會提示：

(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

輸入：1 （這里要求你設置新建字段的默認值，它會在新建這個字段的同時把默認值也添加上去，）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()
>>>

這里面不好修改

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文件為時：

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

設置為True時，字段可以為空。設置為False時，字段是必須填寫的。字符型字段CharField和TextField是用空字符串來存儲空值的。如果為True，字段允許為空，默認不允許.

null

設置為True時，django用Null來存儲空值。日期型、時間型和數(shù)字型字段不接受空字符串。所以設置IntegerField，DateTimeField型字段可以為空時，需要將blank，null均設為True。如果為True，空值將會被存儲為NULL，默認為False。如果想設置BooleanField為空時可以選用NullBooleanField型字段。

(env8) D:\Desktop\env8\Scripts\mysite>python manage.py makemigrations就不會有下面的提示
(env8) D:\Desktop\env8\Scripts\mysite>python manage.py migrate 就行了中間不會設置數(shù)據(jù)類型（很容易出錯）（若要設置默認值）

三、數(shù)據(jù)庫設計是整個網(wǎng)站開發(fā)的核心

補充：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'（添加字段的數(shù)據(jù)類型格式）
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>

以上這篇django 在原有表格添加或刪除字段的實例就是小編分享給大家的全部內(nèi)容了，希望能給大家一個參考，也希望大家多多支持腳本之家。

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