Question

我正在尝试通过Django管理信息中心访问（非托管）模型。该模型没有主键，而是在三个字段中唯一。

class MyObjectView(models.Model):
    solution_id = models.IntegerField(blank=True, null=True)
    scenario_id = models.IntegerField(blank=True, null=True)
    object_id = models.CharField(max_length=256, blank=True, null=True)
    description= models.CharField(max_length=1000, blank=True, null=True)
    year_of_creation = models.DateField(blank=True, null=True)

    class Meta:
        managed = False  # Created from a view. Don't remove.
        db_table = 'myobject_view'

虽然我能够访问管理仪表板中的所有项目列表，但当我尝试查看一个特定项目时，却收到错误消息：

get（）返回多个MyObjectView －返回4个！

根据documentation，我尝试在UniqueConstraint类中添加Meta，但约束似乎没有任何作用，并且上述错误仍然存在：

    class Meta:
        managed = False  # Created from a view. Don't remove.
        db_table = 'myobject_view'
        constraints = [
            models.UniqueConstraint(fields=['solution_id', 'scenario_id', 'object_id '], name='unique_object'),
        ]

这是解决get() returned more than one错误的正确方法吗？约束即使在非托管模型上也应该起作用吗？

Answer 1

我认为如果对象不受管理，则在Meta中添加UniqueConstraint不会在数据库中插入任何约束。

您需要捕获异常：

try:
    the_object = MyObjectView.objects.get(
        object_id=object_id, scenario_id=scenario_id, solution_id=solution_id
    )
    return the_object # or do something different
except MyObjectView.MultipleObjectsReturned:
    # multiple objects have the three same values
    # manage that case
    return None # just as example

看看对MultipleObjectsReturned exception的引用

Answer 2

Another approach is to add .first() to your get(). That guarantees you will get a single result (or None), and will avoid errors at that point.

If the duplicates are a problem it sounds like you need to investigate how they are being created, fix that and then do some clear up.

在Django管理员中使用UniqueConstraint解决“ get（）返回多个错误”的错误

2 个答案: