如何将 Django QuerySet 转换为列表

发布于12月13日

我有以下几点:

answers = Answer.objects.filter(id__in=[answer.id for answer in answer_set.answers.all()])

然后稍后:

for i in range(len(answers)):
    # iterate through all existing QuestionAnswer objects
    for existing_question_answer in existing_question_answers:
        # if an answer is already associated, remove it from the
        # list of answers to save
        if answers[i].id == existing_question_answer.answer.id:
            answers.remove(answers[i])           # doesn't work
            existing_question_answers.remove(existing_question_answer)

我收到一个错误:

'QuerySet' object has no attribute 'remove'

我try 了各种方法将QuerySet转换为标准的集合或列表.毫无办法.

我怎样才能从QuerySet中删除一项，这样它就不会从数据库中删除它，也不会返回新的QuerySet(因为它在一个不起作用的循环中)？

推荐答案

您可以这样做:

import itertools

ids = set(existing_answer.answer.id for existing_answer in existing_question_answers)
answers = itertools.ifilter(lambda x: x.id not in ids, answers)

阅读when QuerySets are evaluated并注意，将整个结果加载到内存(例如通过list())是不好的.

参考:itertools.ifilter

Update关于 comments :

有多种方法可以做到这一点.其中一个(就内存和时间而言可能不是最好的)是做完全相同的事情:

answer_ids = set(answer.id for answer in answers)
existing_question_answers = filter(lambda x: x.answer.id not in answers_id, existing_question_answers)