Django的UniqueConstraint [英] Django UniqueConstraint

问题描述

我有以下模型: AppVersion ， App & DeployApp .在 AppVersion 模型中，用户可以将APK文件上传到文件系统.我正在使用 pre_save 信号来阻止为特定的 App 上载具有相同 version_code 的APK文件，如下所示:

I have the models AppVersion, App & DeployApp. In the AppVersion model users can upload APK files to the filesystem. I am using a pre_save signal to prevent uploading APK files with the same version_code for a specific App like this:

@receiver(pre_save, sender=AppVersion)
def prevent_duplicate_version_code(sender, instance, **kwargs):
    qs = AppVersion.objects.filter(app_uuid=instance.app_uuid, version_code=instance.version_code)
    if qs.exists():
        raise FileExistsError("Version code has to be unique for a specific app")

此信号可以满足我的要求，除了在尝试在桥表 DeployApp 中创建对象时还会引发错误.

This signal does what I want, except it also raises the error when I am trying to create an object in the bridge-table DeployApp.

# models.py

class App(models.Model):
    app_uuid = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False, db_index=True)
    app_name = models.CharField(max_length=100)


class AppVersion(models.Model):
    app_version_uuid = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False, db_index=True)
    app_uuid = models.ForeignKey(App, on_delete=models.CASCADE, related_name='app_versions')
    app_version_name = models.CharField(max_length=100)
    version_code = models.IntegerField(blank=True, null=True, editable=False)
    source = models.FileField(upload_to=get_app_path, storage=AppVersionSystemStorage()) 


class DeployApp(models.Model):
    deploy_app_uuid = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False, db_index=True)
    app_version = models.ForeignKey(AppVersion, on_delete=models.CASCADE)
    device_group = models.ForeignKey(DeviceGroup, on_delete=models.CASCADE)
    release_date = UnixDateTimeField()

我的猜测是，在创建 DeployApp 的对象时，也会保存相关的 AppVersion ，因此会调用 pre_save 信号并引发例外.

My guess is that when creating an object of DeployApp the related AppVersion is also saved and thus the pre_save signal is called and raises the Exception.

我还尝试为 AppVersion 模型覆盖 save()方法，但结果相同.

I also tried to override the save() method for the AppVersion model but the results are the same.

如何确保仅在创建新的 AppVersion 实例时发生该异常，而在添加或编辑 DeployApp 实例时该异常不会发生?

How do I make sure that the Exception only happens upon creating a new AppVersion instance and does not happen when adding or editing a DeployApp instance?

推荐答案

感谢贝尔·布朗(Bear Brown)的建议，解决了该问题.我删除了信号，然后将 UniqueConstraint 添加到 AppVersion 模型中，如下所示:

Solved it thanks to Bear Brown his suggestion. I removed the signal and added UniqueConstraint to the AppVersion model like this:

class Meta:
    db_table = 'app_version'
    constraints = [
        models.UniqueConstraint(fields=['app_uuid', 'version_code'], name='unique appversion')
    ]

这篇关于Django的UniqueConstraint的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！