如何将模型从一个 django 应用程序迁移到新的应用程序中? [英] How do I migrate a model out of one django app and into a new one?

问题描述

我有一个包含四个模型的 django 应用程序.我现在意识到这些模型之一应该在一个单独的应用程序中.我确实为迁移安装了南，但我不认为这是它可以自动处理的事情.如何将旧应用中的模型之一迁移到新应用中?

I have a django app with four models in it. I realize now that one of these models should be in a separate app. I do have south installed for migrations, but I don't think this is something it can handle automatically. How can I migrate one of the models out of the old app into a new one?

另外，请记住，我将需要这是一个可重复的过程，以便我可以迁移生产系统等.

Also, keep in mind that I'm going to need this to be a repeatable process, so that I can migrate the production system and such.

推荐答案

如何使用南迁.

假设我们有两个应用:通用和特定:

How to migrate using south.

Lets say we got two apps: common and specific:

myproject/
|-- common
|   |-- migrations
|   |   |-- 0001_initial.py
|   |   `-- 0002_create_cat.py
|   `-- models.py
`-- specific
    |-- migrations
    |   |-- 0001_initial.py
    |   `-- 0002_create_dog.py
    `-- models.py

现在我们想将模型 common.models.cat 移动到特定的应用程序(确切地说是 specific.models.cat).首先在源代码中进行更改，然后运行:

Now we want to move model common.models.cat to specific app (precisely to specific.models.cat). First make the changes in the source code and then run:

$ python manage.py schemamigration specific create_cat --auto
 + Added model 'specific.cat'
$ python manage.py schemamigration common drop_cat --auto
 - Deleted model 'common.cat'

myproject/
|-- common
|   |-- migrations
|   |   |-- 0001_initial.py
|   |   |-- 0002_create_cat.py
|   |   `-- 0003_drop_cat.py
|   `-- models.py
`-- specific
    |-- migrations
    |   |-- 0001_initial.py
    |   |-- 0002_create_dog.py
    |   `-- 0003_create_cat.py
    `-- models.py

现在我们需要编辑两个迁移文件:

Now we need to edit both migration files:

#0003_create_cat: replace existing forward and backward code
#to use just one sentence:

def forwards(self, orm):
    db.rename_table('common_cat', 'specific_cat') 

    if not db.dry_run:
        # For permissions to work properly after migrating
        orm['contenttypes.contenttype'].objects.filter(
            app_label='common',
            model='cat',
        ).update(app_label='specific')

def backwards(self, orm):
    db.rename_table('specific_cat', 'common_cat')

    if not db.dry_run:
        # For permissions to work properly after migrating
        orm['contenttypes.contenttype'].objects.filter(
            app_label='specific',
            model='cat',
        ).update(app_label='common')

<小时>

#0003_drop_cat:replace existing forward and backward code
#to use just one sentence; add dependency:

depends_on = (
    ('specific', '0003_create_cat'),
)
def forwards(self, orm):
    pass
def backwards(self, orm):
    pass

现在两个应用程序迁移都意识到了变化，生活也少了一点:-)在迁移之间建立这种关系是成功的关键.现在，如果你这样做:

Now both apps migrations are aware of the change and life sucks just a little less :-) Setting this relationship between migrations is key of success. Now if you do:

python manage.py migrate common
 > specific: 0003_create_cat
 > common: 0003_drop_cat

将同时进行迁移和

python manage.py migrate specific 0002_create_dog
 < common: 0003_drop_cat
 < specific: 0003_create_cat

将向下迁移.

请注意，对于架构升级，我使用了通用应用程序，而对于降级，我使用了特定应用程序.那是因为这里的依赖是如何工作的.

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