model修改字段出错问题解决

起因

修改了表结构以后执行python3 manage.py migrate 报错:

django.db.utils.OperationalError: (1091, "Can't DROP 'email'; check that column/key exists")

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所以进数据库把对应的表删除了,想着重新生成这张表. 
删除表以后执行:

python3 manage.py makemigrations
python3 manage.py migrate

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还是不能生成表,提示:No changes detected

处理过程

首先删除了app对应目录下的数据库对应的文件和缓存文件:

$ rm -rf migrations/ __pycache__/

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重新执行:

$ python3 manage.py makemigrations
No changes detected
$~/code/django/blogproject$ python3 manage.py makemigrations comments
Migrations for 'comments':
  comments/migrations/0001_initial.py
    - Create model Comment
$~/code/django/blogproject$ python3 manage.py migrate
Operations to perform:
  Apply all migrations: admin, auth, blog, comments, contenttypes, sessions, users
Running migrations:
  No migrations to apply.

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进入数据库发现仍然没有生成表.

然后发现有一张django_migrations表,里面记录这有关创建表的记录,删除对应的数据表:

delete from django_migrations where app='yourappname';

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重新执行生成数据库命令:

$ python3 manage.py makemigrations comments
No changes detected in app 'comments'
$~/code/django/blogproject$ python3 manage.py  migrate comments
Operations to perform:
  Apply all migrations: comments
Running migrations:
  Applying comments.0001_initial... OK

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数据表顺利生成.

结论

在执行 
python3 manage.py makemigrations 
python3 manage.py migrate 
操作的时候,不仅会创建0001_initial.py对应的模型脚本,还会创建一个数据库记录创建的模型.如果想重新生成数据库,需要两个地方都做删除.