python - Django查询没有返回值怎么办？它给我错误

Question

to_friend = User.objects.filter(username=friend_q)[0:1]

如果“friend_q”不在 User.username 中...它会报错。推荐的策略是什么？

谢谢

Answer 1

如果 friend_q 不是数据库中的用户，to_friend 将等于一个空列表。

>>> from django.contrib.auth.models import User
>>> User.objects.filter(username='does-not-exist')
[]

但是，最好使用 get() 方法来查找特定条目:

>>> User.objects.get(username='does-exist')
<User: does-exist>
>>> User.objects.get(username='does-not-exist')
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/usr/lib/python2.5/django/db/models/manager.py", line 120, in get
  File "/usr/lib/python2.5/django/db/models/query.py", line 305, in get
DoesNotExist: User matching query does not exist.

您现在可以捕获 DoesNotExist 异常并采取适当的措施。

try:
   to_friend = User.objects.get(username=friend_q)
except User.DoesNotExist:
   # do something, raise error, ...