How to query as GROUP BY in django?

Solution 1:

If you mean to do aggregation you can use the aggregation features of the ORM:

from django.db.models import Count
result = (Members.objects
    .values('designation')
    .annotate(dcount=Count('designation'))
    .order_by()
)

This results in a query similar to

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

and the output would be of the form

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

If you don't include the order_by(), you may get incorrect results if the default sorting is not what you expect.

If you want to include multiple fields in the results, just add them as arguments to values, for example:

    .values('designation', 'first_name', 'last_name')

References:

• Django documentation: values(), annotate(), and Count
• Django documentation: Aggregation, and in particular the section entitled Interaction with default ordering or order_by()

Solution 2:

An easy solution, but not the proper way is to use raw SQL:

results = Members.objects.raw('SELECT * FROM myapp_members GROUP BY designation')

Another solution is to use the group_by property:

query = Members.objects.all().query
query.group_by = ['designation']
results = QuerySet(query=query, model=Members)

You can now iterate over the results variable to retrieve your results. Note that group_by is not documented and may be changed in future version of Django.

And... why do you want to use group_by? If you don't use aggregation, you can use order_by to achieve an alike result.

Solution 3:

You can also use the regroup template tag to group by attributes. From the docs:

cities = [
    {'name': 'Mumbai', 'population': '19,000,000', 'country': 'India'},
    {'name': 'Calcutta', 'population': '15,000,000', 'country': 'India'},
    {'name': 'New York', 'population': '20,000,000', 'country': 'USA'},
    {'name': 'Chicago', 'population': '7,000,000', 'country': 'USA'},
    {'name': 'Tokyo', 'population': '33,000,000', 'country': 'Japan'},
]

...

{% regroup cities by country as countries_list %}

<ul>
    {% for country in countries_list %}
        <li>{{ country.grouper }}
            <ul>
            {% for city in country.list %}
                <li>{{ city.name }}: {{ city.population }}</li>
            {% endfor %}
            </ul>
        </li>
    {% endfor %}
</ul>

Looks like this:

• India
  • Mumbai: 19,000,000
  • Calcutta: 15,000,000
• USA
  • New York: 20,000,000
  • Chicago: 7,000,000
• Japan
  • Tokyo: 33,000,000

It also works on QuerySets I believe.

source: https://docs.djangoproject.com/en/2.1/ref/templates/builtins/#regroup

edit: note the regroup tag does not work as you would expect it to if your list of dictionaries is not key-sorted. It works iteratively. So sort your list (or query set) by the key of the grouper before passing it to the regroup tag.