一、如果models.py文件為時(shí)：
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timestamp = models.DateTimeField('保存日期') |
會(huì)提示：
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(env8) D:\Desktop\env8\Scripts\mysite>python manage.py makemigrationsYou are trying to add a non-nullable field 'timestamp' to article without a default; 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(shè)置新建字段的默認(rèn)值，它會(huì)在新建這個(gè)字段的同時(shí)把默認(rèn)值也添加上去，）Select an option: 1
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Please enter the default value now, as valid PythonThe 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
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(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(shí)：
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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
設(shè)置為True時(shí)，字段可以為空。設(shè)置為False時(shí)，字段是必須填寫的。字符型字段CharField和TextField是用空字符串來(lái)存儲(chǔ)空值的。如果為True，字段允許為空，默認(rèn)不允許.
null
設(shè)置為True時(shí)，django用Null來(lái)存儲(chǔ)空值。日期型、時(shí)間型和數(shù)字型字段不接受空字符串。所以設(shè)置IntegerField，DateTimeField型字段可以為空時(shí)，需要將blank，null均設(shè)為True。如果為True，空值將會(huì)被存儲(chǔ)為NULL，默認(rèn)為False。如果想設(shè)置BooleanField為空時(shí)可以選用NullBooleanField型字段。
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(env8) D:\Desktop\env8\Scripts\mysite>python manage.py makemigrations就不會(huì)有下面的提示(env8) D:\Desktop\env8\Scripts\mysite>python manage.py migrate 就行了中間不會(huì)設(shè)置數(shù)據(jù)類型（很容易出錯(cuò)）（若要設(shè)置默認(rèn)值） |
三、數(shù)據(jù)庫(kù)設(shè)計(jì)是整個(gè)網(wǎng)站開發(fā)的核心
補(bǔ)充：timestamp = models.DateTimeField('保存日期')
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(env8) D:\Desktop\env8\Scripts\mysite>python manage.py makemigrationsYou are trying to add a non-nullable field 'timestamp' to article without a default; 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.pySelect an option: 1Please enter the default value now, as valid PythonThe 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 migrateOperations to perform: Synchronize unmigrated apps: staticfiles, ckeditor_uploader, messages, ckeditor, bootstrap3 Apply all migrations: admin, blog, contenttypes, auth, sessionsSynchronizing 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-packages\django\db\models\fields\__init__.py:1474: RuntimeWarning: DateTimeField Article.timestamp received a naive datetime (2017-12-16 05:04:31) while time zone support 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(shí)例就是小編分享給大家的全部?jī)?nèi)容了，希望能給大家一個(gè)參考，也希望大家多多支持服務(wù)器之家。
原文鏈接：https://blog.csdn.net/JackLiu16/article/details/78819194
