如何从连接表中获取多个值

Question

如何获取特定用户订阅的所有课程的所有规律？

class Law(models.Model):
    name  = models.CharField('Nome', max_length=100)
    slug = models.SlugField('Atalho')
    description = models.TextField('Description', blank = True, null=True)

class Course(models.Model):
    name  = models.CharField('Nome', max_length=100)
    slug = models.SlugField('Atalho')
    description = models.TextField('Descrição', blank = True, null=True)
    laws = models.ManyToManyField(Law, related_name='law_course')


class Subscription(models.Model):    
    STATUS_CHOICES=(
        (
            (0, 'Pendente'),
            (1, 'Approved'),
            (2, 'Canceled'),
        )
    )
    user = models.ForeignKey(settings.AUTH_USER_MODEL,on_delete=models.CASCADE, verbose_name="Usuário", related_name="inscricao") #inscricao é criado no usuario
    course = models.ForeignKey(Course, on_delete=models.CASCADE, verbose_name="Course", related_name="subscription")
    status = models.IntegerField(
        'Status', choices=STATUS_CHOICES, default = 0, blank=True
        )

    class Meta:
        unique_together = (('user','course'))

因此，用户可以订阅一门或多门课程。每门课程都有一个或多个定律。

我有一个页面需要列出特定用户订阅的每门课程的所有法律，前提是订阅已获批准 (status = 1)。例子：用户 John 订阅了 2 门课程：课程 A 和课程 B。

Course A laws: law1, law2, law3
Course B laws: law1, law20, law30

因此，当约翰登录时，我需要显示课程的规律和课程名称：

law1 - Course A, Course B
law2 - Course A
law3 - Course A
law20 - Course B
law30 - Course B

请注意，我无法展示law 1两次，但我展示了包含此法则的每门课程。

我已经尽力说清楚了。提前谢谢

Answer 1

您可以使用集来存储法则（最终将是唯一的）。

laws_set = set()
subscriptions = Subscription.objects.filter(user=your_user, status=1)

对于每个订阅，获取课程，然后获取与该课程对应的所有法律。

for subscription in subscriptions:
    laws = subscription.course.laws.all() 

    for law in laws:
        laws_set.add(law)

现在laws_set中的每个法则都可以打印对应的课程了。

for law in laws_set:
    print(law.name, end='')
    for course in law.law_course.all(): # Since law_course is the related name
        print(course.name, end='')
    print('\n')

如何从连接表中获取多个值

How to get multiple values from joined tables

django

django-orm