Django ORM: How to compare concatenated columns?

Data and Databases
1

I’m working on a Django project and I need help with a specific database query. My model has three fields: first_part, second_part, and full_text. I want to find all records where full_text is not equal to the combination of first_part and second_part.

In raw SQL, it would look like this:

SELECT * FROM my_table WHERE full_text != CONCAT(first_part, second_part)

But I’m not sure how to translate this into Django’s ORM. I know about filter() and exclude(), but they usually work with fixed values, not comparisons between columns.

Is there a way to do this comparison using Django ORM? I’d prefer not to use raw SQL if possible.

Thanks for any help or suggestions!

2

Ooh, interesting question! Have u tried using F() expressions? They’re super cool for comparing fields. maybe something like:

MyModel.objects.exclude(full_text=Concat(‘first_part’, ‘second_part’))

Not sure if that’d work exactly, but it mite be a good starting point. wat do u think? Has anyone else tried somethin similar?

3

Here’s an alternative approach that might suit your needs. You can use the ExpressionWrapper and Value classes to ensure proper type casting while performing the concatenation. For example:

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

MyModel.objects.annotate(
    combined=ExpressionWrapper(
        Concat('first_part', Value(''), 'second_part'),
        output_field=CharField()
    )
).exclude(full_text=F('combined'))

This method creates an annotated ‘combined’ field and then excludes records where full_text matches this field. It proves particularly useful when different field types are involved or when further operations on the concatenated result are needed.

4

hey, i’ve dealt with this before! u can use annotate() and then filter(). try this:

MyModel.objects.annotate(combined=Concat(‘first_part’, ‘second_part’)).filter(~Q(full_text=F(‘combined’)))

this should grab all records where full_text isnt the same as first_part+second_part. lemme kno if it works!