我当前的项目使用 multi-table inheritance models :
from django.db import models
class Place(models.Model):
name = models.CharField(max_length=50)
address = models.CharField(max_length=80)
class Restaurant(Place):
serves_hot_dogs = models.BooleanField(default=False)
serves_pizza = models.BooleanField(default=False)
class Cinema(Place):
sells_tickets = models.BooleanField(default=False)
sells_popcorn = models.BooleanField(default=False)
我想切换到abstract base classes反而。由于我的模型已经部署,我需要编写一些自定义迁移来将上述模式转换为这个模式:from django.db import models
class AbstractPlace(models.Model):
name = models.CharField(max_length=50)
address = models.CharField(max_length=80)
class Meta:
abstract = True
class Restaurant(AbstractPlace):
serves_hot_dogs = models.BooleanField(default=False)
serves_pizza = models.BooleanField(default=False)
class Cinema(AbstractPlace):
sells_tickets = models.BooleanField(default=False)
sells_popcorn = models.BooleanField(default=False)
有没有人对实现这一目标的步骤有任何建议?
最佳答案
我最近解决了这个确切的问题,我通过在下面的代码块中编写和运行迁移来解决这个问题 - 松散地转换为适合您的情况的模型。
我很确定不可能改变旧的 Restaurant
的表和 Cinema
直接模型,就好像您尝试向它们添加字段一样,它们将与基础模型的现有字段发生冲突,并且如果您尝试通过例如,将派生模型与基础模型“分离”通过手动设置 abstract=True
在基本模型的 options
, Django 报告无法找到 Restaurant
的基本模型和 Cinema
. (据我所知,这些问题可能是由错误引起的。)为了规避这个问题,我为派生模型创建了新表,将旧表中的数据复制到新表中,删除旧表,并重命名了新表以匹配旧表的名称。
我从 Django 生成的代码中获得了下面的大部分代码,可以通过创建一个临时迁移(在使用下面的代码创建一个之前)来复制这些代码,该迁移只删除 Restaurant
, Cinema
和 Place
, 正在运行 makemigrations
,并复制 CreateModel()
s 和 AlterField()
s(用于指向 Restaurant
或 Cinema
的相关字段)来自生成的迁移。
为了记录,我使用的是 Django 3.1.4。
from django.db import migrations, models
def copy_objects_from_restaurant_and_cinema_to_restaurant_tmp_and_cinema_tmp(apps, schema_editor):
Restaurant_Tmp = apps.get_model('<app name>', 'Restaurant_Tmp')
Cinema_Tmp = apps.get_model('<app name>', 'Cinema_Tmp')
Restaurant = apps.get_model('<app name>', 'Restaurant')
Cinema = apps.get_model('<app name>', 'Cinema')
# The `_meta.fields` list includes the PK
copy_objects_from_old_model_to_new_model(Restaurant, Restaurant_Tmp, Restaurant_Tmp._meta.fields)
copy_objects_from_old_model_to_new_model(Cinema, Cinema_Tmp, Cinema_Tmp._meta.fields)
def copy_objects_from_old_model_to_new_model(old_model, new_model, fields_to_copy):
field_names = [field.name for field in fields_to_copy]
for old_obj in old_model.objects.all():
old_obj_field_dict = {
field_name: getattr(old_obj, field_name)
for field_name in field_names
}
new_model.objects.create(**old_obj_field_dict)
def copy_objects_from_restaurant_tmp_and_cinema_tmp_to_restaurant_and_cinema(apps, schema_editor):
Restaurant_Tmp = apps.get_model('<app name>', 'Restaurant_Tmp')
Cinema_Tmp = apps.get_model('<app name>', 'Cinema_Tmp')
Restaurant = apps.get_model('<app name>', 'Restaurant')
Cinema = apps.get_model('<app name>', 'Cinema')
copy_objects_from_old_model_to_new_model(Restaurant_Tmp, Restaurant, Restaurant_Tmp._meta.fields)
copy_objects_from_old_model_to_new_model(Cinema_Tmp, Cinema, Cinema_Tmp._meta.fields)
class Migration(migrations.Migration):
dependencies = [
('<app name>', '<last migration>'),
]
operations = [
migrations.CreateModel(
name='Restaurant_Tmp',
fields=[
('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
('name', models.CharField(max_length=50)),
('address', models.CharField(max_length=80)),
('serves_hot_dogs', models.BooleanField(default=False)),
('serves_pizza', models.BooleanField(default=False)),
],
options={
'abstract': False,
},
),
migrations.CreateModel(
name='Cinema_Tmp',
fields=[
('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
('name', models.CharField(max_length=50)),
('address', models.CharField(max_length=80)),
('sells_tickets', models.BooleanField(default=False)),
('sells_popcorn', models.BooleanField(default=False)),
],
options={
'abstract': False,
},
),
migrations.RunPython(copy_objects_from_restaurant_and_cinema_to_restaurant_tmp_and_cinema_tmp, migrations.RunPython.noop),
# Update foreign keys to reference the non-abstract models directly,
# instead of through the (automatically generated) `place_ptr` field of the old models
<
Run `migrations.AlterField()` here for each related field (like ForeignKey) of other models that point to Restaurant or Cinema,
but change their `to` argument from e.g. `<app name>.restaurant` to `<app name>.restaurant_tmp`
>
migrations.RunPython(migrations.RunPython.noop, copy_objects_from_restaurant_tmp_and_cinema_tmp_to_restaurant_and_cinema),
migrations.DeleteModel(
name='Restaurant',
),
migrations.DeleteModel(
name='Cinema',
),
migrations.DeleteModel(
name='Place',
),
migrations.RenameModel(
old_name='Restaurant_Tmp',
new_name='Restaurant',
),
migrations.RenameModel(
old_name='Cinema_Tmp',
new_name='Cinema',
),
]
请注意,我最初编写的迁移仅使用 SQLite 进行了测试;其他数据库管理系统可能不接受如此大量的迁移操作,您可能不得不将其拆分为多个迁移。 (我有点不确定究竟是什么导致了这个问题,但我记得我在 PostgreSQL 上遇到过它。)如果这能解决您的问题,请告诉我! 😊
关于python - 从多表继承模型迁移到Django中的抽象基类,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/65355459/