Django；是否可以为queryset设置默认值

Question

employee = Employee.objects.filter('age' = 99)

我们假设此查询集为空。

如果我使用employee[0]，它将返回索引超出范围的错误，那么这里是否可以将None作为默认值？

`employee[0] or None`? # This won't work, but this is what I mean.

Answer 1

如果只想获取一个实例，请使用 get ，而不要使用filter:

employee = Employee.objects.get(age = 99)

如果不存在，您将得到一个Employee.DoesNotExist异常，您需要捕获该异常。如果有一个超过99岁的员工，您将收到一个Employee.MultipleObjectsReturned异常，您可能想捕获该异常。

如果您感到懒惰，总是有django-annoying的get_object_or_None!

from annoying.functions import get_object_or_None

obj = get_object_or_None(Employee, age=99)

如果您不想使用所有的django-annoying，可以随时在某处添加get_object_or_None，它看起来像这样:

def get_object_or_None(klass, *args, **kwargs):
    """
    Uses get() to return an object or None if the object does not exist.

    klass may be a Model, Manager, or QuerySet object. All other passed
    arguments and keyword arguments are used in the get() query.

    Note: Like with get(), a MultipleObjectsReturned will be raised if
    more than one object is found.
    """
    queryset = _get_queryset(klass)
    try:
        return queryset.get(*args, **kwargs)
    except queryset.model.DoesNotExist:
        return None