django : How can i check if an object is exist in a many-to-many relation?

Question

I have a model named Post that has some fields like this :

class Post(models.Model):
    title = models.CharField(max_length=500)
    slug = models.SlugField(allow_unicode=True , unique=True , null=True , blank=True)
    likes = models.ManyToManyField(User , blank=True , help_text="amount of likes")
    likes_count = models.IntegerField(default=0 , help_text="amount of likes")

    def __str__(self):
        return self.title

and I have a view that needs to check if the user is in "likes" relation and do some stuff . But I don't know what to do ! this is my view:

def Like_view(request , slug):
    post = get_object_or_404(Post , slug=slug)
    if not request.user in post.likes:
        post.likes.add(request.user)
        post.likes_count += 1
        post.save()
    else:
        post.likes.remove(request.user)
        post.likes_count -= 1
        post.save()

Answer 1

you dont need to save count of likes.

in your case:

likes_count = post.likes.count()
# or 
likes_count = post.likes.aggregate(likes_count=Count('*')).get('likes_count')

more here:

https://docs.djangoproject.com/en/4.2/ref/models/querysets/#aggregation-functions

For your view I prefer to delete like, if returns nothing - it means you don't have a like and you can create it:

def Like_view(request , slug):
    if not Post.likes.through.objects.filter(post__slug=slug, user = post.user).delete():
        get_object_or_404(Post , slug=slug).likes.add(request.user)

And my opinion, the sheme can be better, with boolean checkbox in through model. In this case you can do only one DB call:

Post.likes.through.objects.filter(post__slug=slug, user = post.user).update(is_like=Q(is_like=False))