Django group object by the first character of a column

Question

I\'m trying to group records by the character of name field of each record and limit the items in each group, here is what I have came up with:

desi         


        

Answer 1

From the comment in the other answer:

I was actually looking for a way to implement Group By First Character in django orm

I would do it in following 3 steps:

1. Annotate each record with first letter of the name field. For that you could use Substr function along with Lower

   from django.db.models.functions import Substr, Lower 
   qs = User.objects.annotate(fl_name=Lower(Substr('name', 1, 1)))
   

2. Next, group all the records with this first letter and get the count of ids. This can be done by using annotate with values:

   # since, we annotated each record we can use the first letter for grouping, and 
   # then get the count of ids for each group
   from django.db.models import Count
   qs = qs.values('fl_name').annotate(cnt_users=Count('id'))
   

3. Next, you can order this queryset with the first letter:

   qs = qs.order_by('fl_name')
   

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Combining all these in one statement:

from django.db.models.functions import Substr, Lower
from django.db.models import Count 

qs = User.objects \
         .annotate(fl_name=Lower(Substr('name', 1, 1))) \
         .values('fl_name') \
         .annotate(cnt_users=Count('id')) \
         .order_by('fl_name')

At the end, your queryset would look something like this. Do note, that I converted first character to lower case while annotating. If you don't need that, you can remove the Lower function:

[{'fl_name': 'a', 'cnt_users': 12}, 
 {'fl_name': 'b', 'cnt_users': 4},
 ...
 ...
 {'fl_name': 'z', 'cnt_users': 3},]

If, you need a dictionary of letter and count:

fl_count = dict(qs.values('fl_name', 'cnt_users'))
# {'a': 12, 'b': 4, ........., 'z': 3}