python - 如何检查查询集是否为空？

Question

分页码:

try:
    page = paginator.page(page_number)
    print(page.object_list)

所以下面的输出是我的分页 print(page.object_list) 的结果:

<QuerySet [<Comment: I can't believe it's happeinig>, <Comment: Just trying to fill up the comments>, <Comment: Another one!>, <Comment: Evenmore noe>, <Comment: Something>, <Comment: Lol>, <Comment: Are comments showing up?>, <Comment: Great for the economy.>, <Comment: honestly>, <Comment: Even though the the onlyEven though the only one to udnertstnaf!>]>
<QuerySet [<Comment: Yeah it's crazy how fast aswell. It's very awesome how it's doing atm. >]>
<QuerySet []>
<QuerySet [<Comment: Sure>, <Comment: No worries>]>
<QuerySet []>
<QuerySet []>
<QuerySet [<Comment: attempt 2!>]>
<QuerySet [<Comment: Attempt 3!>]>
<QuerySet []>
<QuerySet [<Comment: 12>]>
<QuerySet []>
<QuerySet [<Comment: Somewhere?>]>
<QuerySet []>
<QuerySet [<Comment: lol>]>
<QuerySet []>
<QuerySet [<Comment: 12>]>
<QuerySet []>

如您所见，我有空的查询集，这些会导致我的代码出现错误。因此，我想遍历这些查询集并找出空的。我尝试添加这个 for 循环:

for i in page.object_list:
    if len(i) < 0:

但我得到一个错误:

TypeError at /news/11/
object of type 'Comment' has no len()

任何帮助表示赞赏。

如果查询集为空，则尝试删除它:

try:
    page = paginator.page(page_number)
    if page.object_list:
        pass
    else:
        page.delete()

错误:

AttributeError at /news/11/
'CustomPage' object has no attribute 'delete'  

Answer 1

您可以使用 if 子句直接测试 QuerySet。这将导致 QuerySet 被评估。空查询集(或空列表)是 falsy:

page = paginator.page(page_number)
if page.object_list:
    ...

如果您想在 QuerySet 上进行迭代，则无需测试是否为空。只需使用 for 子句:

for obj in page.object_list: # empty QuerySet gets zero iterations
   ...