基于外键强制唯一约束

Question

我对一个列强制了一个唯一的约束，由于该约束是在整个表上强制的，所以有没有办法根据外键使一个列唯一

型号

class Bucket(models.Model):
    """This class represents the bucket model"""
    title = models.CharField(max_length=255, blank=False, unique=True)

class Bucketlist(models.Model):
    """This class represents the bucketlists model"""
    bucket = models.ForeignKey(Bucket, on_delete=models.CASCADE, 
             related_name='bucketlists')
    name = models.CharField(max_length=255, blank=False, unique=True)

例如 我创建了2个bucket（bucket 1和bucket 2）

创建了以下bucketlists

>>> Bucketlist.objects.create(bucket=bucket1, name='bucketlist1')
>>> Bucketlist.objects.create(bucket=bucket1, name='bucketlist2')

正在尝试在bucket 2中创建bucketlist1

>>> Bucketlist.objects.create(bucket=bucket2, name='bucketlist1')
IntegrityError: duplicate key value violates unique constraint "myapp_bucketlist_name"

Answer 1

看起来您希望Bucketlist上的name字段是唯一的，但仅适用于那些属于相同Bucket的对象

为此，您可以查看Django的unique_together元选项（documentation）

在您的情况下，它看起来像：

class Bucketlist(models.Model):
    """This class represents the bucketlists model"""
    bucket = models.ForeignKey(Bucket, on_delete=models.CASCADE, 
                               related_name='bucketlists')
    name = models.CharField(max_length=255, blank=False)

    class Meta:
        unique_together = (("bucket", "name"),)

注意从name字段中删除了unique=True