How to Find Rows with Duplicate Field Values Using Django ORM?

Django Query for Rows with Duplicate Field Values

Suppose we have a Django model with a non-unique field. We need to select all rows from the model that have at least one duplicate value for that field.

Plain SQL Approach

One possible solution is to use plain SQL:

SELECT *
FROM literal
WHERE name IN (
    SELECT name
    FROM literal
    GROUP BY name
    HAVING COUNT(*) > 1
);

Django ORM Approach

Using Django's ORM, we can achieve the same result with a combination of values(), annotate(), order_by(), and filter():

from django.db.models import Count

dupes = Literal.objects.values('name') \
                    .annotate(Count('id')) \
                    .order_by() \
                    .filter(id__count__gt=1)

As the above code returns a ValuesQuerySet, we need to convert it to a regular QuerySet to use it as a filter:

duplicates = Literal.objects.filter(name__in=[item['name'] for item in dupes])

This approach ensures that we only select rows with duplicate name values.

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