Create Django Table displaying information about users - django

Question

I am currently using django 1.8 and I'd like to create a more intelligent way to display information about users. Say I have something like this:
class User(models.Model):
name = models.CharField()
class Invitation(models.Model):
inviter = models.ForeignKey(User)
invitee = models.ForeignKey(User)
I want to create a field that is the unique number of user's an inviter has invited. I could see how this could be done with something like set("SELECT invitee FROM INVITATIONS WHERE inviter = 'my-user';"), but if I want this displayed in the admin panel, is there a simple way to present this?
Also, I would want this done for every user, so it feels like there is a simple way to make a field generated for every user in the table.

Answer 1

First, let's setup proper related_name- it'll help reduce a lot of confusion in the code.
class Invitation(models.Model):
inviter = models.ForeignKey(User, related_name="invitation_sent")
invitee = models.ForeignKey(User, related_name="invitation_recv")
With the related_name setup, we can do queries such as
user = User.objects.get(pk=1)
# retrieve all invitation objects sent by this user
user.invitation_sent.all()
# retrieve all invitation objects received by this user
user.invitation_recv.all()
Now we can actually count the number of unique invitations a user has sent out quite easily:
# count number of distinct invitee for user
user.invitation_sent.all().values('invitee').distinct().count()
Next, we can actually count the number of unique users a user has invited in a single database query for all users:
user_list = User.objects.all().annotate(
uniq_inv=Count('invitation_sent__invitee', distinct=True)
)
Each user object returned will have an additional property called uniq_inv which contains the count of unique users the user has invited
for user in user_list:
print(user.name + ' invited ' + user.uniq_inv + ' unique users')
To apply this to the admin interface, you'll need to override get_queryset method:
class MyAdmin(admin.ModelAdmin):
...
list_display = [..., 'uniq_inv']
def uniq_inv(self, obj):
return obj.uniq_inv
uniq_inv.short_description = 'Unique Invitees'
def get_queryset(self, request):
qs = super(MyAdmin, self).get_queryset(request)
qs = qs.annotate(uniq_inv=Count('invitation_sent__invitee', distinct=True))
return qs

Answer 2

You can use annotate, which allows to add calculated fields to a queryset.
Models:
class User(models.Model):
name = models.CharField()
class Invitation(models.Model):
inviter = models.ForeignKey(User,related_name="inviter_user")
invitee = models.ForeignKey(User,related_name="invited_user")
Queryset:
from django.db.models import Count
q = Invitation.objects.annotate(count_invitee=Count('invitee')).all()
Now "count_invitee" field has the number for each invitation object.
If you want to filter invitee from the user side.
For a single user:
User.objects.get(pk=1).invited_user.all.count()
For all users queryset:
User.objects.annotate((count_invitee=Count('invited_user')).all()