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.
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.