Django模型字段在添加新字段时基于同一模型中的另一个字段添加默认值

Question

我有这个领域，

job_created = models.DateTimeField(auto_now_add=True)

现在我想添加这样的东西，如何将默认值基于 post_created 本身。我希望第一个 last_modified 是在创建工作时，我想要类似的东西

last_modified = models.DateTimeField(auto_now=True, default = post_created)

或者，如果我在运行迁移时提供一个默认值，该怎么做？

Answer 1

基本上你不能，但你可以创建一个 data migration

def set_last_modified(apps, schema_editor):
    MyModel = apps.get_model('myapp', 'MyModel')

    for obj in MyModel.objects.all():
        obj.last_modified = obj.post_created
        obj.save()


class Migration(migrations.Migration):

    dependencies = [
        ('myapp', 'previous_migration'),
    ]

    operations = [
        # Doesn't need to do anything in reverse, models have not been changed
        migrations.RunPython(set_last_modified, migrations.RunPython.noop)
    ]

您应该通过运行获取此迁移的模板

migrations --empty yourappname