python - Django 上不必要的自动迁移？

Question

运行 python 3.6 和 Django 3.1.7!

所以我有一个 Django 项目，其中的应用程序的模型如下:

class Department(models.Model_:
   name = models.CharField(max_length=255)

class Person(models.Model):
    first_name = models.CharField(max_length=255)
    last_name = models.CharField(max_length=255)
    department = models.ForeignKey(
        Department, related_name="department_members", on_delete=models.CASCADE
    )

当我运行makemigrations时，我在0001_initial.py上得到了这个:

class Migration(migrations.Migration):

    initial = True

    operations = [
        migrations.CreateModel(
            name='Person',
            fields=[
                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('first_name', models.CharField(max_length=255)),
                ('last_name', models.CharField(max_length=255)),
            ],
        ),
        migrations.CreateModel(
            name='Department',
            fields=[
                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('name', models.CharField(max_length=255)),
            ],
        ),
        migrations.AddField(
            model_name='person',
            name='department',
            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='department_members', to='my_app.department'),
        ),
    ]

这一切都很好，但现在我收到了这个红色文本:

Your models have changes that are not yet reflected in a migration, and so won't be applied.

Run 'manage.py makemigrations' to make new migrations, and then re-run 'manage.py migrate' to apply them.

当我再次运行 makemigrations 时，我得到的结果为 0002_auto_20211111_1116.py:

class Migration(migrations.Migration):

    dependencies = [
        ('my_app', '0001_initial'),
    ]

    operations = [
        migrations.AlterField(
            model_name='Department',
            name='id',
            field=models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID'),
        ),
        migrations.AlterField(
            model_name='Person',
            name='id',
            field=models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID'),
        ),
    ]

我没有对 models.py 进行更改，而且我也看不到自动迁移时更改的“id”字段有什么不同。

我总是可以将 0002 留在文件夹中并继续我的生活，但这确实一直困扰着我。是什么向 Django 发出信号表明我的模型发生了某些变化？如何避免创建第二次迁移？

谢谢!

Answer 1

它将主键从 BigAutoField 迁移到 AutoField。可能的原因是因为 django-3.2 ，DEFAULT_AUTO_FIELD setting [Django-doc]已添加到设置中。如果您指定了该设置:

<strong>DEFAULT_AUTO_FIELD</strong> = 'django.db.models.BigAutoField'

然后 Django 将使用 BigAutoField。

如果您随后迁移回 django-3.1 ，那么 Django 不会考虑 DEFAULT_AUTO_FIELD 设置，而是使用 AutoField。由于您没有明确提及主键，这意味着它假设您使用 AutoField，因此会将字段迁移到 AutoField。

如果您不想这样做，可以删除迁移文件，并使用以下命令显式定义 id 字段:

class Department(models.Model):
    id = <strong>models.BigAutoField(</strong>auto_created=True, primary_key=True, serialize=False, verbose_name='ID'<strong>)</strong>
   name = models.CharField(max_length=255)

class Person(models.Model):
    id = <strong>models.BigAutoField(</strong>auto_created=True, primary_key=True, serialize=False, verbose_name='ID'<strong>)</strong>
    first_name = models.CharField(max_length=255)
    last_name = models.CharField(max_length=255)
    department = models.ForeignKey(
        Department, related_name="department_members", on_delete=models.CASCADE
    )