我必须在两个不同的应用程序中调整模型，如app1和app2，在app1中我得到Model1，在app2中我得到BaseModel，Model1就像这个
class Model1(BaseModel):
...
Model1和BaseModel在一个应用程序中，但我将Model1移动到了app2，现在我也想将BaseModel也移动到app2。我的问题是，当我试图将BaseModel移动到app2时，我会收到以下错误：
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：
- 我编写了将BaseModel的表重命名为app2_BaseModel的迁移，然后编写了在app2中创建模型的迁移
- 我创建迁移是为了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本模型时，会出现此错误。
我感谢任何帮助，包括任何其他方式来实现将BaseModel移动到app1的重构想法
Django没有内置的迁移操作，但您可以通过将多个迁移操作拼凑在一起来实现这一点。
迁移不仅会更改数据库，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。密钥使用migrations.SeparateDatabaseAndState。
假设您有以下模型定义：
# 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)
你想迁移到这个：
# 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的表从app1_basemodel重命名为app2_basemodel。这还负责调整basemodel_ptr列上的外键约束 - 在App2中：添加
app2.BaseModel并以app2.BaseModel为基础模型重新创建app2.Model1。这些更改仅对迁移状态执行，并且不会触及数据库 - 在App1中：将
app1.BaseModel从迁移状态中删除。同样，没有数据库更改
以下是代码中的情况：
# 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。我担心，如果你有其他与Model1相关的模型，这可能会变得更加复杂。
免责声明：我已经用SQLite和PostgreSQL测试过这些，但使用它的风险自负！在对生产数据运行备份之前，请确保您有备份。
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，您可以考虑编写一个自定义迁移操作。
我试图从状态中删除model1，它成功了以下是我为使其发挥作用所做的工作(一些名称是从我所写的内容更改的(：
-
从状态中删除模型1
state_operations = [migrations.DeleteModel('Model')] operations =[migrations.SeparateDatabaseAndState(state_operations=state_operations)] -
重命名BaseModel的表(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
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 ), ] -
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)]
这个解决方案对我有效，在SQLite和PSQL上没有任何数据丢失测试。