Django为什么在确保列表存在后，我在请求列表中的第一项时会得到一个索引器？

Question

我对自己可能做错的事很不放心

html

if follows_answers.exists():
    previous_question = follows_answers[0].question
else:
    previous_question = current_question.follows_question.all()[0]

相关追溯

/srv/local/quizapp/quiz/views.py in previous_question_url
       277. previous_question = follows_answers[0].question

Local Vars

Variable    
follows_answers   [<Answer: Blue>]

/home/quizapp/.virtualenvs/quizapp/local/lib/python2.7/site-packages/django/db/models/query.py in __getitem__
        return list(qs)[0]

Local Vars

Variable
qs                []
k                 0
self              [<Answer: Blue>]

Answer 1

查询集被延迟计算，可能列表转换没有触发计算。请改为显式地follows_answers.all()[0].question