How to concatenate two model fields in a Django QuerySet?

Question

Consider a table called DataTable. It has two fields: A and B.

I want to return all rows from this table, and annotating a field called C which is a concatenation of A and B fields.

Here is what I have tried:

from django.db.models import CharField, Value
from .models import DataTable

def Test(request):
    query = DataTable.objects.all().annotate(C=Value('A' + '-' + 'B', 
          output_field=CharField()))
    # the rest of the function...

The problem here is that C is literally just the string literal "A - B" for every returned row.

I want to concatenate the values of A and B fields.

Ammonia

did you use F()? F('A') – Venireman

Answer 1

looks like you need concat:

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

query = DataTable.objects.annotate(C=Concat('A', 
          Value('-'), 'B', output_field=CharField()))

Quench

Perfect...now how do add a hyphen in between A and B – Ammonia

Since you can't use a CONCAT function in an index because its behavior changes based on settings, how would you concat in Django using the || operator? – Reeher

Answer 2

Basically there are two approaches to achieve it.

First one:
First of all, you need to import the following expressions.

from django.db.models import F, Value, Func

then, concatenate the fields as below:

ann_concat = Customer.objects.annotate(
            fullName = Func(F('first_name'), Value(' '),F('last_name'), function= 'CONCAT'))

In above example, I have concatenated first name and last name into a new field called fullName.

Second one: This approach is way shorter than the first one you only need to import Concat() and Value() for making the spaces functions.

from django.db.models.functions import Concat


  short_syntax = Customer.objects.annotate(full_name = Concat('first_name',Value(' '),'last_name'))

Traffic

Answer 3

You can do so with Value() and of course Concat django

Value is to set the white space or -, try the following:

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


def Test(request):
     query = DataTable.objects.annotate(C=Concat('A',Value('-') ,'B',
                 output_field=CharField())
      # the rest of the function...

Obtuse

F not need for Concat ) – Quench

perfect, added in Value(' - ') instead of Value(' '). – Ammonia

@Obtuse glad to help you – Quench