如何将Django QuerySet转换为列表

Question

我有以下内容：

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

然后再：

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'

我尝试了各种方法将QuerySet转换为标准集或列表。没用。

我如何从QuerySet中删除一个项目，以便它不会从数据库中删除它，并且不返回新的QuerySet（因为它处于循环状态，因此无法使用）？

Answer 1

你可以这样做：

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)

在评估QuerySet时阅读，请注意，将整个结果加载到内存中（例如通过list()）是不好的。

参考： itertools.ifilter

关于评论的更新：

有多种方法可以做到这一点。一种（在内存和时间方面可能不是最好的一种）是做完全相同的：

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)