[Django]-How to count the amount of objects in a django joined table?

In your UserList instead using model, use this queryset:

from django.db.models import Count

class UserList(ListView):
    queryset = Users.objects.annotate(num_assets=Count('assets'))

and define your user field like so:

user = models.ForeignKey('Users', blank=True, null=True, related_name='assets')

then from template:

{{ user.num_assets }}

Also please remember, it’s a good practice to use singular model names, to avoid confusion with reverse relation names..

You are doing weird things. Use the related managers that django give you instead. I’ll write the view as a function based view:

views.py

def users_list(request):
    object_list = Users.objects.all()
    render(request, 'mytemplate.html', { 'object_list': object_list })

You can get the counts directly in the template via the RelatedManager:

mytemplate.html

{% for user in object_list %}
 <tr>
     <td>{{ user.id }}</td>
     <td>
         {{ user.assets_set.count }}
     </td>
 </tr>
{% endfor %}

You could also annotate with a count. But learn to float before you swim

BTW, you should call your models “User” and “Asset”, not Users and Assets.

You need to use select_related(), count() and pass user instance as argument to class method like so:

@classmethod
def user_assets(cls,user):
    return Assets.objects.select_related('Users').filter(user=user).count()

and then use it like so:

user = Users.objects.all()[0] # some user object (this assumes you have at least one user)
Assets.user_assets(user)

this should work fine, you can try it in the shell.

In your context this will be used like this:

user = self.model.all()[0] # or get or filter just get some particular user
context['user_assets'] = Assets.user_assets(user)

EDIT: added links, and Users.object.all() instead of Users.object.get(), also added example suited to your specific use case.