DJANGO: Mass update field by adding a prefix

Question

I wish to update a Django model field of objects in a queryset. To be specific, I want to add a prefix on one of the fields i.e. if an object has a name like 'Wilson', I want to prefix it with 'OLD', then it will become 'OLDWilson'.

I can think of the following using loops:

my_objs = MyObjects.objects.filter(name='some_name') # This has over 40000 records
for obj in my_objs:
    obj.name = 'OLD{0}'.format(obj.name)
    obj.save()

I was hoping of a more elegant way to take advantage of the UPDATE method as specified here: Django Mass Update

Something like the following:

MyObjects.objects.filter(name='some_name').update(name='OLD+name_here')

Any pointers on how I can achieve this?

Answer 1

I know this question is almost 5 years old. But, with hopes that this helps the answer be more visible - here goes.

Use Concat from django.db.models.functions like so:

from django.db.models.functions import Concat
from django.db.models import Value
MyObjects.objects.filter(name='some_name').update(name=Concat(Value'OLD', 'name'))

That last line returns the number of rows affected by the update.

Answer 2

This actually works in the latest version of Django as of May 2022

from django.db.models import Value
from django.db.models.functions import Concat

query = MyObjects.objects.filter(name='some_name')
query.update(name=Concat(Value("OLD"), "name"))