Django ManyToMany overwritten when saving CustomUser model

Question

Overview

I'm in the process of creating a friendship model to track users who follow each other. I've created a CustomUser model that extends AbstractUser and a separate UserRelationship model which is used to create/track the interaction. I also have a signal.py file that handles the actual saving between the two models (CustomUser & UserRelationship).

The Issue

When creating a friendship (User with PK=1 follows user with PK=2), the Following ManyToMany field for user with PK=1 is updated correctly, however if user with PK=1 updates their profile, all ManyToMany fields are wiped.

Models CustomUser

class CustomUser(AbstractUser):
    # Model manager
    objects = CustomUserManager()
    # Local
    email = models.CharField(max_length=80, blank=True)
    biography = models.CharField(max_length=100, blank=True)
    photo = models.ImageField(
        upload_to="users/%Y/%m/%d/",
        blank=True,
        default="static/images/default_profile_pic.png",
    )
    hidden = models.BooleanField(default=False)
    # ForeignKey
    following = models.ManyToManyField(
        "CustomUser", related_name="followings", blank=True
    )
    follower = models.ManyToManyField(
        "CustomUser", related_name="followers", blank=True
    )
    blocked = models.ManyToManyField("CustomUser", related_name="blocks", blank=True)
    blocked_user_visible = models.ManyToManyField(
        "CustomUser", related_name="block_user_visible", blank=True
    )
    hidden_request = models.ManyToManyField(
        "CustomUser", related_name="hidden_requests", blank=True
    )

    def get_relationships(self):
        return self.relationship.all()

    def get_following(self):
        return self.followings.all()

    def get_relationships_number(self):
        return self.relationship.all().count()

    def __str__(self):
        return self.username

    def get_absolute_url(self):
        return f"/users/{self.username}"

UserRelationships Model

class UserRelationship(models.Model):
    STATUS_CHOICES = (
        ("sent", "sent"),
        ("accepted", "accepted"),
        ("deleted", "deleted"),
        ("blocked", "blocked"),
    )
    # Local
    status = models.CharField(max_length=8, choices=STATUS_CHOICES, blank=True)
    updated = models.DateTimeField(auto_now=True)
    date_added = models.DateTimeField(auto_now_add=True)
    # ForeignKey
    # You have received a request from
    user = models.ForeignKey(
        settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name="from_user"
    )
    # You have sent a request to
    following = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        null=True,
        related_name="to_user",
    )

    def __str__(self):
        return f"{self.user} sent a friend request to {self.following}, status == {self.status}"

Example: JSON after UserRelationship created

{
    "url": "http://localhost:8000/api/v1/users/1/",
    "pk": 1,
    "username": "test",
    "first_name": "removed forStackOverflow",
    "last_name": "removed forStackOverflow",
    "email": "removed forStackOverflow",
    "hidden": false,
    "following": [
        44
    ],
    "follower": [],
    "blocked": [],
    "hidden_request": [],
    "photo": "https://azure.blob.core.windows.net/media/users/2020/06/28/test-36b9cdd1da48477dbb738b2f63ffca5f.jpg",
    "biography": "Friday Aug 7"
}

Example: JSON after updating the biography field for user test (following no longer shows user's pk "44")

{
    "url": "http://localhost:8000/api/v1/users/1/",
    "pk": 1,
     "username": "test",
    "first_name": "removed forStackOverflow",
    "last_name": "removed forStackOverflow",
    "email": "removed forStackOverflow",
    "hidden": false,
    "following": [],
    "follower": [],
    "blocked": [],
    "hidden_request": [],
    "photo": "https://azure.blob.core.windows.net/media/users/2020/06/28/test-36b9cdd1da48477dbb738b2f63ffca5f.jpg",
    "biography": "This was updated"
}

Signals.py

@receiver(post_save, sender=UserRelationship)
def add_friend(sender, instance, created, **kwargs):
    """Signal function that responds to status of either
    accepted, sent, blocked"""
    sender_ = instance.user
    receiver_ = instance.following

    if instance.status == "accepted":
        # If receiver's pk is already in sender's following M2M
        if sender_.following.filter(pk=receiver_.pk).exists():
            # Print (turn to HttpResponse)
            print(f"You're already friends with {receiver_.username}")
        # If sender's status is hidden
        if receiver_.hidden:
            instance.status = "sent"
            # Add sender to receiver's hidden_request M2M (for notification & approvals)
            receiver_.hidden_request.add(sender_.pk)
            receiver_.save()
        else:
            # Else sender_ now follows the receiver
            sender_.following.add(receiver_.pk)
            # Receiver_ also now follows the sender
            # Optional (Facebook style friendship, remove for twitter style friendship)
            # receiver_.follower.add(sender_.pk)
            # Save sender_
            sender_.save()
            # Save receiver_
            receiver_.save()

Edit I forgot to mention, I am using the admin portal to create the UserRelationship and I am also using Django-Rest-Framework to update the biography field for user with PK=1. I have also tried removing the save portion within the else block of the add_friend function in signals.py leaving only the add portion and the results were the same.

Answer 1

I resolved this by changing my PUT to PATCH