Django迁移文件在其他应用程序？ [英] Django migration file in an other app?

问题描述

下面简单介绍一下Django项目：

 < root> /lib/python2.7/site-packages/ externalapp / shop 
< root> / myapp 
  

myapp 还通过添加几个字段来扩展 externalapp.shop.models 模型。 manage.py makemigrations 确实生成了以下模式迁移文件，名为 0004_auto_20150410_2001.py ：

 从__future__导入unicode_literals 
从django.db导入模型，迁移
 
 
类迁移（迁移。迁移）：
 
＃__init__被我添加为尝试如何告诉django的
＃迁移加载程序操作是针对不同的应用程序
 def __init __（self，name，app_label）：
 super（Migration ，self）.__ init __（name，'shop'）
 
 dependencies = [
（'myapp'，'__first__'），
（'shop'，'0003_auto_20150408_0958'） ，
] 
 
 operations = [
 migrations.AddField（
 model_name ='product'，
 name ='vat'，
 field = models.ForeignKey（to ='myapp.VAT'，null = True），
），
] 
  

如果以上迁移模式默认放置在< root> /lib/python2.7/site-packages/externalapp/shop/migrations / 路径中，管理。 py迁移成功，表字段正确添加。

但是，如果我将上述迁移文件移动到 myapp /迁移/ ，跟随 manage.py migrate 失败，

django。 core.management.base.CommandError：检测到冲突的迁移（myapp中的0001_initial，0004_auto_20150410_2001）。
要修复它们运行'python manage.py makemigrations --merge'

错误消息我不太明白并建议 makemigrations --merge 失败与预期：

ValueError：找不到set的共同祖先（[u'0001_initial '，u'0004_auto_20150410_2001']）

我试图覆盖 migrations.Migration .__ init __ 更改派生的 app_label ，但似乎迁移加载器忽略它。

如何调整迁移文件，使其可以从其他申请？
原因是在生产中 externalapp 源不能被直接触摸，只能被读取。

解决方案

要在Django项目周围移动迁移文件，例如注入其他应用程序的模型，您需要确保在 django.db.migrations.Migration descendant：

• 显式设置应用程序名称，因为迁移装载程序会由迁移文件所在的应用程序自动导出，并尝试对不同的模型执行操作，否则


• 通知迁移记录器为其他应用程序提供迁移，或者仍然将迁移视为未应用程序（有关应用迁移的记录存储在表中，目前命名为 django_migrations ）

我已经解决了迁移初始值设置中的问题，

 从django.db导入迁移
 
 TARGET_APP ='shop' ＃application label migration for 
 
 class Migration（migrations.Migration）：
 
 def __init __（self，name，app_label）：
＃overriding application operating on 
 super（Migration，self）.__ init __（name，TARGET_APP）
 
＃指定它取代
＃的原始迁移文件，或者让迁移加载器对未应用的迁移感到困惑
替换=（（TARGET_APP，__module __。rsplit（'。'，1）[ -  1]），）
  

<

如果可能，渴望听到更好/更简单的解决方案。

Let's imagine a following simplified Django project:

<root>/lib/python2.7/site-packages/externalapp/shop
<root>/myapp

myapp also extends externalapp.shop.models models by adding a few fields. manage.py makemigrations did generated following schema migration file called 0004_auto_20150410_2001.py:

from __future__ import unicode_literals
from django.db import models, migrations


class Migration(migrations.Migration):

    # __init__ is added by me as an attempt how to tell django's
    # migration loader operations are for the different application
    def __init__(self, name, app_label):
        super(Migration, self).__init__(name, 'shop')

    dependencies = [
        ('myapp', '__first__'),
        ('shop', '0003_auto_20150408_0958'),
    ]

    operations = [
        migrations.AddField(
            model_name='product',
            name='vat',
            field=models.ForeignKey(to='myapp.VAT', null=True),
        ),
    ]

If the above migration schema is placed in <root>/lib/python2.7/site-packages/externalapp/shop/migrations/ path by default, manage.py migrate succeeds and table fields are correctly added.

However if I do move the above migration file into myapp/migrations/, following manage.py migrate fails with

django.core.management.base.CommandError: Conflicting migrations detected (0001_initial, 0004_auto_20150410_2001 in myapp). To fix them run 'python manage.py makemigrations --merge'

error message I can't quite understand and suggested makemigrations --merge fails with expected:

ValueError: Could not find common ancestor of set([u'0001_initial', u'0004_auto_20150410_2001'])

I've tried to override migrations.Migration.__init__ to alter derived app_label but seems migration loader ignores it.

How adjust migration file so it can work from other application ? The reason is in production externalapp sources can't be directly touched, are read only.

解决方案

To move a migration file around a Django project, like in case of injecting models of other applications, you need to ensure in your django.db.migrations.Migration descendant:

• explicitly set application name, as migrations loader derives it automatically by app where migration file resides and would attempt to perform operations on different models otherwise
• notify migrations recorder it provides migration for other application or it would still consider migration as unapplied (records about applied migrations are stored in a table, currently named django_migrations)

I've solved the issue in migration initializer which may look like:

from django.db import migrations

TARGET_APP = 'shop'    # application label migration is for

class Migration(migrations.Migration):

    def __init__(self, name, app_label):
        # overriding application operated upon
        super(Migration, self).__init__(name, TARGET_APP)

    # specify what original migration file it replaces
    # or leave migration loader confused about unapplied migration
    replaces = ((TARGET_APP, __module__.rsplit('.', 1)[-1]),)

It does work for me and find it enough generic way.

Eager to hear about a better/simpler solution if possible.

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