将 Django 模型移动到另一个应用程序，该应用程序是另一个模型的父模型

Question

我必须在两个不同的应用程序（如 app1 和 app2）中使用 django 模型，在 app1 中我得到了 Model1，在 app2 中我得到了 BaseModel 并且 Model1 是这样的

class Model1(BaseModel):
...

Model1 和 BaseModel 在一个应用程序中，但我将 Model1 移至 app2，现在我也想将 BaseModel 移至 app2。我的问题是当我尝试将 BaseModel 移动到 app2 时出现此错误：

Cannot resolve bases for [<ModelState: 'app1.model1'>]
This can happen if you are inheriting models from an app with migrations (e.g. contrib.auth)
 in an app with no migrations; see https://docs.djangoproject.com/en/2.1/topics/migrations/#dependencies for more

我做的很简单：

我编写迁移以将 BaseModel table 重命名为 app2_basemodel 然后我编写迁移以在 app2
我创建迁移以更改用于继承的字段basemodel_ptr
我将 BaseModel 代码移动到 app2 并通过从 app1 迁移删除 BaseModel

此方法适用于移动 Model1，但当我尝试移动此基础模型时出现此错误。

我感谢任何帮助，包括实现将 BaseModel 移动到 app1 的重构想法的任何其他方法

Answer 1

Django 没有为此提供内置的迁移操作，但您可以通过拼凑多个迁移操作来实现。

迁移不仅会改变数据库，还会保持所有模型的状态。您必须确保状态与数据库保持同步，这会使事情变得有点复杂。关键是使用 migrations.SeparateDatabaseAndState.

假设您有这些模型定义：

# app1/models.py
from django.db import models

class BaseModel(models.Model):
    base_field = models.CharField(max_length=64)

# app2/models.py
from django.db import models
from app1.models import BaseModel

class Model1(BaseModel):
    model_field = models.CharField(max_length=64)

并且您想迁移到此：

# app1/models.py empty
# app2/models.py

from django.db import models

class BaseModel(models.Model):
    base_field = models.CharField(max_length=64)

class Model1(BaseModel):
    model_field = models.CharField(max_length=64)

您必须创建三个迁移：

在 App1 中：将 app1.BaseModel 的 table 从 app1_basemodel 重命名为 app2_basemodel。这也负责调整 basemodel_ptr 列上的外键约束。
在 App2 中：添加 app2.BaseModel 并使用 app2.BaseModel 作为基础模型重新创建 app2.Model1。这些更改仅针对 迁移状态 进行，请勿触及数据库！
在 App1 中：从迁移状态中删除 app1.BaseModel。同样，没有数据库更改。

代码如下：

# app1/migrations/0002_rename_basemodel_table.py
from django.db import migrations, models


class Migration(migrations.Migration):
    atomic = False
    dependencies = [
        ('app1', '0001_initial'),
    ]
    operations = [
        migrations.AlterModelTable(
            name='BaseModel',
            table='app2_basemodel'
        ),
    ]

# app2/migrations/0002_change_basemodel.py
from django.db import migrations, models
import django.db.models.deletion


class Migration(migrations.Migration):

    dependencies = [
        ('app2', '0001_initial'),
        ('app1', '0002_rename_basemodel_table')
    ]

    state_operations = [
        migrations.CreateModel(
            name='BaseModel',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('base_field', models.CharField(max_length=64)),
            ],
        ),
        migrations.DeleteModel(
            name='Model1',
        ),
        migrations.CreateModel(
            name='Model1',
            fields=[
                ('basemodel_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='app2.BaseModel')),
            ],
            bases=('app2.basemodel',),
        ),
    ]
    database_operations = [
    ]
    operations = [
        migrations.SeparateDatabaseAndState(
            database_operations,
            state_operations
        )
    ]

# app1/0003_remove_basemodel.py
from django.db import migrations, models


class Migration(migrations.Migration):

    dependencies = [
        ('app1', '0002_rename_basemodel_table'),
        ('app2', '0002_change_basemodel')
    ]

    state_operations = [
        migrations.DeleteModel(
            name='BaseModel',
        ),
    ]
    operations = [
        migrations.SeparateDatabaseAndState(
            database_operations=None,
            state_operations=state_operations
        )
    ]

显然，您必须调整这些迁移以反映您的实际模型。恐怕如果你有其他模型与 Model1 有关系，这可能会变得更加复杂。

免责声明： 我已经用 SQLite 和 PostgreSQL 测试了这些，但使用它需要您自担风险！确保在运行生产数据之前有一个备份。

之前：

$ python manage.py dbshell
SQLite version 3.19.3 2017-06-27 16:48:08
Enter ".help" for usage hints.
CREATE TABLE IF NOT EXISTS "app1_basemodel" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "base_field" varchar(64) NOT NULL);
CREATE TABLE IF NOT EXISTS "app2_model1" ("basemodel_ptr_id" integer NOT NULL PRIMARY KEY REFERENCES "app1_basemodel" ("id") DEFERRABLE INITIALLY DEFERRED, "model_field" varchar(64) NOT NULL);
...

$ python manage.py shell
Python 3.7.0 (default, Aug 22 2018, 15:22:33)
[Clang 9.1.0 (clang-902.0.39.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from app2.models import Model1
>>> Model1.__bases__
(<class 'app1.models.BaseModel'>,)
>>> Model1.objects.create(base_field='a', model_field='A')
<Model1: Model1 object (1)>
>>> Model1.objects.create(base_field='b', model_field='B')
<Model1: Model1 object (2)>
>>>

之后：

sqlite> .schema
...
CREATE TABLE IF NOT EXISTS "app2_basemodel" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "base_field" varchar(64) NOT NULL);
CREATE TABLE IF NOT EXISTS "app2_model1" ("basemodel_ptr_id" integer NOT NULL PRIMARY KEY REFERENCES "app2_basemodel" ("id") DEFERRABLE INITIALLY DEFERRED, "model_field" varchar(64) NOT NULL);
...

>>> from app2.models import Model1
>>> Model1.__bases__
(<class 'app2.models.BaseModel'>,)
>>> for obj in Model1.objects.all():
...  print(obj.base_field, obj.model_field)
...
a A
b B

或者，您可以查看 writing a custom migration operation。

Answer 2

我尝试从状态中删除 model1 并且成功了这是我为使其正常工作所做的工作（一些名称已从我所写的问题中更改）：

正在从状态中删除模型 1

state_operations = [migrations.DeleteModel('Model')]
operations =[migrations.SeparateDatabaseAndState(state_operations=state_operations)]

为 BaseModel 重命名 table（您需要为 SQLite 设置 atomic=True）

operations = [
migrations.AlterModelTable(
    name='basemodel',
    table='first_basemodel',
),

]

将模型移动到第一个应用程序

def update_contentypes(apps, schema_editor):
    ContentType = apps.get_model('contenttypes', 'ContentType')
    db_alias = schema_editor.connection.alias

    qs = ContentType.objects.using(db_alias).filter(app_label='second', model='basemodel')
    qs.update(app_label='first')


def update_contentypes_reverse(apps, schema_editor):
    ContentType = apps.get_model('contenttypes', 'ContentType')
    db_alias = schema_editor.connection.alias

    qs = ContentType.objects.using(db_alias).filter(app_label='first', model='basemodel')
    qs.update(app_label='second')

class Migration(migrations.Migration):

dependencies = [
    ('first', '0002_delete_model_from_state'),
    ('second', '0002_auto_20181218_0717')
]
state_operenterations = [
        migrations.CreateModel(
            name='BaseModel',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('name', models.CharField(max_length=200)),
            ],
        ),
    ]

database_operations = [
    migrations.RunPython(update_contentypes, update_contentypes_reverse),
]

operations = [
    migrations.SeparateDatabaseAndState(
        state_operations=state_operations,
        database_operations=database_operations
    ),
]

正在从状态中删除 app2 中的 BaseModel

state_operations = [
migrations.DeleteModel('BaseModel'),
]

operations = [
migrations.SeparateDatabaseAndState(state_operations=state_operations)
]

移动代码并添加回 Model1

state_operations = [migrations.CreateModel(
name='Model',
fields=[
('basemodel_ptr', models.OneToOneField(auto_created=True, on_delete=models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='first.BaseModel')),
    ('title', models.CharField(max_length=200)),
],
bases=('first.basemodel',),),]

operations = [migrations.SeparateDatabaseAndState(state_operations=state_operations)]

这个解决方案对我很有效，没有在 SQLite 和 PSQL 上测试过任何数据丢失。

将 Django 模型移动到另一个应用程序，该应用程序是另一个模型的父模型

move a django model to another app which is parent model for another model

python

django

refactoring

django-migrations