外键模型的django计数

Question

您好，我想显示我的问题模型的答案计数

我的模特：

class Question(models.Model):

    text = models.TextField()
    title = models.CharField(max_length=200)
    date = models.DateTimeField(default=datetime.datetime.now)
    author = models.ForeignKey(CustomUser)
    tags = models.ManyToManyField(Tags)

    def __str__(self):
        return self.title


class Answer(models.Model):

    text = models.TextField()
    date = models.DateTimeField(default=datetime.datetime.now)
    likes = models.IntegerField(default=0)
    author = models.ForeignKey(CustomUser)
    question = models.ForeignKey(Question)

我的看法：

def all_questions(request):

    questions = Question.objects.all()
    answers = Answer.objects.filter(question_id=questions).count()

    return render(request, 'all_questions.html', {
            'questions':questions, 'answers':answers })

现在视图显示所有答案的计数。我如何通过Question 模型过滤它？

Answer 1

您可以使用.annotate()获取与每个question关联的answers的计数。

from django.db.models import Count
questions = Question.objects.annotate(number_of_answers=Count('answer')) # annotate the queryset

通过这样做，每个question 对象将有一个额外的属性number_of_answers，其值answers 与每个question 相关联。

questions[0].number_of_answers # access the number of answers associated with a question using 'number_of_answers' attribute

最终代码：

from django.db.models import Count

def all_questions(request):
    questions = Question.objects.annotate(number_of_answers=Count('answer'))
    return render(request, 'all_questions.html', {
            'questions':questions})

在您的模板中，您可以执行以下操作：

{% for question in questions %}
    {{question.number_of_answers}} # displays the number of answers associated with this question

Answer 2

见docs
您可以对查询进行注释，例如：

from django.db.models import Count
questions = Question.objects.annotate(num_answer=Count('answer'))

但是，将代码重构为此。 删除答案计数：

def all_questions(request):
    questions = Question.objects.all()
    return render(request, 'all_questions.html', {'questions':questions })

现在，在all_question.html。只需使用：

{% for question in questions %}
    Title: {{question.title}}
    Count Answers: {{question.answer_set.all|length}}
    {% for answer in question.answer_set.all %}
        {{answer.text}}
    {% endfor %}
{% endfor %}

效率更高。