如何在一个查询中从 3 个不同的表中检索所有数据？

Question

我想做以下事情，但我不明白该怎么做：

为每个班级显示该班级的所有学生，为该班级的每个学生显示该学生的所有统计数据。

我的模型是：

class Classes(models.Model):
    name = models.CharField(max_length=256)
    day_and_time= models.CharField(max_length=256)

    def __str__(self):
        return self.name

    def get_absolute_url(self):
        return reverse("classesapp:class_detail", kwargs={"pk": self.pk})


class Students(models.Model):
    name = models.CharField(max_length=256)
    student_class =  models.ForeignKey(
        Classes, related_name = 'students', on_delete=models.SET_NULL, null=True
    )

    def __str__(self):
        return self.name

    def get_absolute_url(self):
        return reverse("classesapp:student_detail", kwargs={"pk": self.pk})

class Statistics(models.Model):
    student= models.ForeignKey(
        Students, related_name='statistics', on_delete=models.CASCADE, null=True
    )
    date = models.DateField(blank=True, null=True)
    dictation_score = models.FloatField()
    writing_score = models.FloatField()
    test_score = models.FloatField()
    grammar_score = models.FloatField()
    in_class_performance = models.FloatField()

    class Meta:
        ordering = ["-date"]

    def get_absolute_url(self):
        return reverse("classesapp:classes_list")

我的 ClassesDetailView 是：

class ClassesDetailView(DetailView):
    queryset  = models.Classes.objects.select_related('statistics')
    context_object_name = "class_detail"
    model = models.Classes
    template_name = "classesapp/class_detail.html"

我知道我必须覆盖查询集，我尝试了 select_relatad 但仍然找不到解决方案。 提前谢谢！

Answer 1

它将运行 2 个循环。根据您的模型，class 可以有很多 students 和 student 可以有很多 statistics。
更新：

result = []  

for student in Students.objects.all(): 

    student_data = {}
    student_data['student_name'] = student.name
    student_data['class_name'] = student.student_class.name
    statistics_data = []  

    for statistics in student.statistics.all():  

        statistics_data.append({
        'dictation_score': statistics.dictation_score,
        'writing_score': statistics.writing_score,
        'grammer_score': statistics.grammer_score,
        'in_class_performance': statistics.in_class_performance
        })  

    student_data['statistics_data'] = statistics_data  

result.append(student_data)