python - Can I use Django F() objects with string concatenation?

Question

I want to run a django update through the ORM that looks something like this:

MyModel.objects.filter(**kwargs).update(my_field=F('my_other_field')+'a string')

This causes MySQL to throw an exception. Is there anyway to do this without writing raw SQL?

Answer 1

I had a similar issue; basically I wanted to concatenate two fields to the get the full name of a user. I got it solved this way(but must say that I was using Postgres):

from django.db.models.functions import Concat
from django.db.models import F, Value, CharField

AnyModel.objects.filter(**kwargs).annotate(full_name=Concat(F('model__user_first_name'), Value(' '), F('model__user_last_name'), output_field=CharField()))

where, F('...') evaluates its argument as a query, so you can query a field of the model itself, or span across models as you would do in filter/get, while Value('...') evaluates its argument literally(in my case I needed a space to be placed in between first_name and last_name), and output_field=... specifies the Type of the annotated field(I wanted to be a CharField). For more info, you can read Django docs about Concat

Hope it will be helpful for someone out there. Cheers