django 外鍵模型計數

Question

嗨，我想顯示我的問題模型的答案計數

我的模型：

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 })

現在視圖顯示所有答案的計數。 我如何通過Question模型過濾它？

Answer 1

您可以使用.annotate()獲取與每個question相關的answers計數。

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

通過這樣做，每個question對象將有一個額外的屬性number_of_answers具有與每個question關聯的answers數量的值。

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

最終代碼：

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，您可以執行以下操作：

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

Answer 2

查看文檔
您可以注釋查詢，例如：

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

但是，將代碼重構為此。 刪除答案的數量：

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

現在，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 %}

它更有效率。