Django 与用户默认身份验证 model 和另一个 Model 的关系

Question

I'm developing a web application where users can subscribe to different series of texts, that would be seen inside the system. I want to create a relationship between the User and the SeriesText , so I can grab the current logged user in the VIEW, and just return all of his subscriptions at the dashboard template. An user would be able to subscribe to as many series as he wants.

I'm using the default User model from django.contrib.auth.models , and I'm not sure how to create this relationship.

I read a lot and I think the correct usage here would be Many-to-many (is that correct?), so I tried this, using a pivot table/model called Subscriptions :

from django.contrib.auth.models import User as BaseUserClass

class User(BaseUserClass):
    subscriptions = models.ManyToManyField(SeriesText, through="Subscription")


 class SeriesText(models.Model):
    series_name = models.CharField(max_length=255)
    series_text = models.CharField(max_length=255)
    subbed_users = models.ManyToManyField(User, through="Subscription")


class Subscription(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    series = models.ForeignKey(SeriesText, on_delete=models.CASCADE)

    def subscribe(self, user_id, series_id):
        self.user = user_id
        self.series = series_id
        self.save()

But that didn't seem to work, I got errors even trying to use a User.objects.get(pk=1) , don't really know why.

I'm really confused if I need to put the relationship both ways, like created models.ManyToMany on SeriesText model, and on an extended User model (that I don't even know if that's really the way to do it). I'm not even sure if that the correct way to make a relationship using the default auth user model.

To be able to later also search for all users subscribed to a series, I think that the models.ManyToMany should also be on the SeriesText model, is that also correct?

Can someone help me understand if I'm using the correct relationship (many-to-many), and how to make this relationship? Thanks in advance, I'm pretty new to Django I'm hitting a wall here.

Answer 1

You only need to add a m2m field on SeriesText . Fundamentally, it doesn't matter which model a many-to-many field is attached to (the database will look the same and the data access will be similar if not identical). Based on my experience, it's better if you don't have to mess with the Django User model:

class SeriesText(models.Model):
    series_name = models.CharField(max_length=255)
    series_text = models.CharField(max_length=255)
    subscribers = models.ManyToManyField(User, related_name='subscriptions')

    def __str__(self):
        return self.series_name

To see how that works, first add some data:

s1 = SeriesText.objects.create(series_name='name1', series_text='text1')
s2 = SeriesText.objects.create(series_name='name2', series_text='text2')

u1 = User.objects.create_user('user1')
u2 = User.objects.create_user(username='user2')
u3 = User.objects.create_user(username='user3')
u4 = User.objects.create_user(username='user4')
u5 = User.objects.create_user(username='user5')

s1.subscribers.add(u1, u2, u3)
s2.subscribers.add(u3, u4, u5)

Then to fetch all subscribers for a SeriesText (I'm fetching the objects from the database here to show that it is not an artefact of the last two lines above - data has been changed in the database):

>>> SeriesText.objects.get(series_name='name1').subscribers.all()
[<User: user1>, <User: user2>, <User: user3>]

>>> SeriesText.objects.get(series_name='name2').subscribers.all()
[<User: user3>, <User: user4>, <User: user5>]

to fetch all subscriptions for a user (we declared that the relation from User to SeriesText should be named subscriptions in the many-to-many field):

>>> User.objects.get(username='user1').subscriptions.all()
[<SeriesText: name1>]
>>> User.objects.get(username='user2').subscriptions.all()
[<SeriesText: name1>]
>>> User.objects.get(username='user3').subscriptions.all()
[<SeriesText: name1>, <SeriesText: name2>]
>>> User.objects.get(username='user4').subscriptions.all()
[<SeriesText: name2>]
>>> User.objects.get(username='user5').subscriptions.all()
[<SeriesText: name2>]

If we hadn't declared the related_name we would have had to use the default:

User.objects.get(username='user1').seriestext_set.all()

which doesn't read as well.