django如何在不进行太多查询的情况下检查此应用程序上是否已存在用户?
假设这些为django模型:django如何在不进行太多查询的情况下检查此应用程序上是否已存在用户?,django,django-queryset,Django,Django Queryset,假设这些为django模型: class Question(): question = charfield() choice = charfield(choices = answer_choice) class Answer(): question = models.foreignkey(Question, related_name = 'answers') answerer = models.foreignkey('auth.User') answ
class Question():
question = charfield()
choice = charfield(choices = answer_choice)
class Answer():
question = models.foreignkey(Question, related_name = 'answers')
answerer = models.foreignkey('auth.User')
answer = models.charfield()
我正在构建一个页面,其中显示100个问题,每个用户可以回答,但不能更改每个问题的答案。对于每个问题,我必须检查回答者
上是否已经存在用户
。然后我制作模板标签:
@寄存器过滤器
定义此用户存在(用户,obj):
obj=obj.answers.filter(answerer\u id=user.id)
返回obj
然后在模板上:
# obj is list of question
{% if not user|this_user_exists:obj %}
# can answer
{% else %}
# cannot answer
{% endif %}
{% if not obj.id in answered_ids %}
# can answer
{% else %}
# cannot answer
{% endif %}
问题是,对于每个问题,它会生成一个查询,所以对于100个问题,它会生成100个查询。我尝试此查询以生成问题question.objects.all()
和question.objects.prefetch\u related('answers')
,但仍然遇到问题。有没有更好的方法在不进行太多查询的情况下实现这一点?为了减少查询,您可以先查询出所需的答案,然后获取所有相关的答案
answers = Answer.objects.select_related('answerer').filter(xxxx)
# fetch related user id's
userids_in_answer = [answer.answerer.id for answer in answers]
# fetch user ids
user_id_set = set(User.objects.filter(id__in=userids_in_answer).values('id', flat=True)
之后,您可以通过
for answer in answers:
if answer.answerer.id in user_id_set:
xxx
查询数量已减少,您可以检查这是否有帮助。在您的视图中:
answered_ids = [ans.question_id for ans in Answer.objects.filter(answerer=request.user)]
在模板中:
# obj is list of question
{% if not user|this_user_exists:obj %}
# can answer
{% else %}
# cannot answer
{% endif %}
{% if not obj.id in answered_ids %}
# can answer
{% else %}
# cannot answer
{% endif %}