How Do I Perform Group By Queries in Django?

Group By Queries in Django

Background

When querying a Django model, you may encounter a scenario where you need to perform a group by operation. Attempting to use .group_by() as you would in SQL results in an error.

Aggregation Features

Instead of using .group_by(), Django provides aggregation methods that allow you to perform complex queries involving groupings. Specifically, Count is useful for counting the occurrences of a particular field.

Example

To group the results by designation and count the occurrences, you would use the following code:

from django.db.models import Count

result = (Members.objects
    .values('designation')
    .annotate(dcount=Count('designation'))
    .order_by()
)

This query is similar to the following SQL statement:

SELECT designation, COUNT(designation) AS dcount
FROM members GROUP BY designation

The output of the Django query would be in the form:

[{'designation': 'Salesman', 'dcount': 2}, 
 {'designation': 'Manager', 'dcount': 2}]

Additional Notes

• Include order_by() to ensure correct sorting.
• To include multiple fields in the results, pass them as arguments to .values().
• Refer to Django's documentation on values(), annotate(), and Count for more information.

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