Django：将具有继承性的模型属性外包给更通用的模型

Question

我注意到，我需要一个基于指定模型的通用模型，下面的例子应该说明我的意思：

之前：

class TextResult(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL, default=1)
    text = models.ForeignKey(Text)
    wpm = models.FloatField(default=0.0)
    accuracy = models.FloatField(default=1.0)

之后：

class TypingResult(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL, default=1)
    wpm = models.FloatField(default=0.0)
    accuracy = models.FloatField(default=1.0)


class TextResult(TypingResult):
    text = models.ForeignKey(Text)

虽然原模型中已经有一些数据了，所以需要将数据迁移到新的模型结构中

Answer 1

以下答案基于此答案(https://stackoverflow.com/a/44148102/4129587)

为了实现这一点，有必要进行手动数据迁移

以下 5 个基本迁移步骤可实现预期结果：

1. 创建新模型TypingResult
2. 在旧模型TextResult 中创建一个对新模型TypingResult 可以为空的新外键
3. 将所有旧属性复制到新模型TypingResult的新实例中
4. 从原始模型中删除包括 id 在内的旧属性
5. 将外键更改为新的主键

可以通过自动生成的新模型迁移来开始迁移

以下代码基于自动生成的迁移并已经过测试

from __future__ import unicode_literals

from django.conf import settings
import django.core.validators
from django.db import migrations, models
import django.db.models.deletion

def copy_text_results_to_typing_results(apps, schema_editor):
    TypingResult = apps.get_model('testapp', 'TypingResult')
    TextResult = apps.get_model('testapp', 'TextResult')
    for text_result in TextResult.objects.all():
        copied_result = TypingResult()
        copied_result.user = text_result.user
        copied_result.wpm = text_result.wpm
        copied_result.accuracy = text_result.accuracy
        copied_result.save()
        text_result.typingresult_ptr = copied_result
        text_result.save()

class Migration(migrations.Migration):

    dependencies = [
        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
        ('testapp', '0001_initial'),
    ]

    operations = [
        migrations.CreateModel(
            name='TypingResult',
            fields=[
                ('id', models.AutoField(auto_created=True, 
                                        primary_key=True,
                                        serialize=False,
                                        verbose_name='ID')),
                ('wpm', models.FloatField(default=0.0)),
                ('accuracy', models.FloatField(default=1.0)),
                ('user', models.ForeignKey(default=1, 
                                           on_delete=django.db.models.deletion.CASCADE,
                                           to=settings.AUTH_USER_MODEL)),
            ],
        ),
        # add the foreign key for the new inherited model,
        # it is allowed to have null values since the actual values have to be
        # copied first to this, it will be changed later
        migrations.AddField(
            model_name='textresult',
            name='typingresult_ptr',
            field=models.OneToOneField(blank=True, null=True, to='testapp.TypingResult'),
        ),
        # copy the old values to the new inherited model
        migrations.RunPython(copy_text_results_to_typing_results),
        # remove the old id and the copied fields from the TextResult model
        migrations.RemoveField(
            model_name='textresult',
            name='accuracy',
        ),
        migrations.RemoveField(
            model_name='textresult',
            name='id',
        ),
        migrations.RemoveField(
            model_name='textresult',
            name='user',
        ),
        migrations.RemoveField(
            model_name='textresult',
            name='wpm',
        ),
        # alter the id of the inherited model to be the new primary key
        migrations.AlterField(
            model_name='textresult',
            name='typingresult_ptr',
            field=models.OneToOneField(auto_created=True,
                                       on_delete=django.db.models.deletion.CASCADE,
                                       parent_link=True,
                                       primary_key=True,
                                       serialize=False,
                                       to='testapp.TypingResult'),
        ),
    ]