如何将Django QuerySet转换为列表 [英] How to convert a Django QuerySet to a list

问题描述

我有以下内容：

  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））：
＃遍历所有现有的QuestionAnswer对象
for existing_question_answers中的existing_question_answer：
＃如果一个答案已经相关联，从
＃的答案列表中删除它，以保存
如果答案[i] .id == existing_question_answer.answer.id：
答案。删除（answer [i]）＃不工作
existing_question_answers.remove（existing_question_answer）


我收到一个错误：

 'QuerySet'对象没有属性'remove'
  

我已经尝试过各种将QuerySet转换为标准等或列表。没有任何工作。

如何从QuerySet中删除一个项目，以便它不会从数据库中删除它，并且不会返回一个新的QuerySet（因为它在

解决方案

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不在ids，答案）
  

阅读 时，djangoproject.com/en/dev/ref/models/querysets/#when-querysets-are-evaluatedrel =noreferrer> 并注意到它不是很好地将整个结果加载到内存中（例如通过 list（））。

参考： itertools.ifilter

更新关于评论：

有很多种方法可以做到这一点。一个（这可能不是最好的记忆和时间）是完全一样的：

  answer_ids = set （answer.id回答答案）
 existing_question_answers =过滤器（lambda x：x.answer.id不在answers_id，existing_question_answers）
  

I have the following:

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

then later:

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)

I get an error:

'QuerySet' object has no attribute 'remove'

I've tried all sorts to convert the QuerySet to a standard set or list. Nothing works.

How can I remove an item from the QuerySet so it doesn't delete it from the database, and doesn't return a new QuerySet (since it's in a loop that won't work)?

解决方案

You could do this:

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)

Read when QuerySets are evaluated and note that it is not good to load the whole result into memory (e.g. via list()).

Reference: itertools.ifilter

Update with regard to the comment:

There are various ways to do this. One (which is probably not the best one in terms of memory and time) is to do exactly the same :

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)

这篇关于如何将Django QuerySet转换为列表的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！