如何从外键相关模型检索属性到另一个外键相关模型？

Question

我在 python 3.10.8 中使用 django 4.1.2。我有三种模型，一种用于用户管理，一种用于问题，另一种用于答案。它们描述如下：

class User(AbstractUser):
    phone_number = models.CharField(max_length=14, unique=True)
    first_name = models.CharField(max_length=40)
    father_name = models.CharField(max_length=40)
    email = models.EmailField(unique=True, required=True)
    age = models.CharField(max_length=3)
    username = models.CharField(max_length=8, required=True)

class Question(models.Model):
    question = models.CharField(
        max_length=500,
        null=False,
        unique=True
    )
    creating_staff = models.ForeignKey(
        User,
        null=False,
        on_delete=models.PROTECT,
        to_field="phone_number",
    )
    options = models.JSONField(null=False)
    correct_option = models.CharField(max_length=250, null=False)
    question_ts = models.DateTimeField(auto_now_add=True, null=False)

    class Meta:
        verbose_name = "Question"

    def __str__(self) -> str:
        return f"{self.question}"


class Answer(models.Model):
    answer = models.CharField(max_length=500, null=False)
    question_answered = models.ForeignKey(
        Question,
        null=False,
        on_delete=models.PROTECT,
        related_name="question_answered"
    )
    answering_user = models.ForeignKey(
        User,
        null=False,
        on_delete=models.PROTECT,
        to_field="phone_number",
        related_name="answerer"
    )
    status = models.BooleanField(null=False)
    answer_ts = models.DateTimeField(auto_now_add=True, null=False)

    class Meta:
        verbose_name = "Answer"

    def __str__(self) -> str:
        return f"{self.answer} -- {self.answering_user}"

这是urls.py 文件：

from django.urls import path

from .views import (AnswerView)

app_name = "commons"

urlpatterns = [
    path("play/", AnswerView.as_view(), name="play"),
]

我正在尝试做的是，每当用户登录并想通过转到 /commons/play/ 来回答一组问题时，在 GET 请求上，我想解析出用户之前回答过的所有问题，并且总是通过从未回答的问题中随机选择 10 个来显示新问题。

到目前为止我所做的是：

import random
from django.shortcuts import (redirect, render)
from django.views import View
from django.contrib import messages
from django.contrib.auth.mixins import LoginRequiredMixin

from .models import (Question, Answer, User)

class AnswerView(LoginRequiredMixin, View):

    def get(self, request):
            answerer = request.user
            total_answers_by_user = Answer.objects.filter(answering_user=answerer)
            questions = Question.objects.all()
            question_list = list()
            for ans in total_answers_by_user:
                for q in questions:
                    if not ans.question_answered == q:
                        question_list.append(q)
            questions_count = question.count()
            try:
                rand_sample = random.sample(range(questions_count), 10)
            except (ValueError, Exception) as e:
                print(f"{e} population for random sample < 10, perhaps new player")
                total_questions = Question.objects.all().count()
                rand_sample = random.sample(range(total_questions), 10)
                questions_to_ask = Question.objects.filter(id__in=rand_sample)
            else:
                questions_to_ask = Question.objects.filter(id__in=rand_sample)

            return render(request, "commons/answer.html", {"questions": questions_to_ask})

但我非常怀疑这是一种检索未回答问题或新问题的有效方法，尤其是当涉及到多个用户时。有没有更好的方法来检索用户之前回答过的所有问题，并且只显示新的或未回答的问题？

感谢您的回复。

Answer 1

要分解您需要做的事情，首先您需要用户回答的问题 ID 列表

answered_qs = (Answer.objects
    .filter(answering_user=answerer)
    .values_list('question_answered_id', flat=True)
    )

然后您想从所有问题集中排除该问题列表

question_list = Question.objects.exclude(pk__in=answered_qs)

使用related_names，可以一次调用完成所有这些。在这里，我们跟随 questions_answered 到字段 answering_user 是我们的请求者的答案集，并排除该集。

questions_list = Question.objects.exclude(question_answered__answering_user=answerer)

如果有一个轻微的性能影响很多的问题，你甚至可以在同一个数据库调用中获得随机的 10 组，例如，

questions_list = (
    Question.objects
    .exclude(question_answered__answering_user=answerer)
    .order_by('?')[:10]
    )