GROUP_CONCAT equivalent in Django

Question

Say I have the following table called fruits:

id | type   | name
-----------------
 0 | apple  | fuji
 1 | apple  | mac
 2 | orange | navel

My goal is to ultimately come up with a count of the different types and a comma-delimited list of the names:

apple, 2, "fuji,mac"
orange, 1, "navel"

This can be easily done with GROUP_CONCAT in MySQL but I'm having trouble with the Django equivalent. This is what I have so far but I am missing the GROUP_CONCAT stuff:

query_set = Fruits.objects.values('type').annotate(count=Count('type')).order_by('-count')

I would like to avoid using raw SQL queries if possible.

Any help would be greatly appreciated!

Thanks! =)

Answer 1

You can create your own Aggregate Function (doc)

from django.db.models import Aggregate

class Concat(Aggregate):
    function = 'GROUP_CONCAT'
    template = '%(function)s(%(distinct)s%(expressions)s)'

    def __init__(self, expression, distinct=False, **extra):
        super(Concat, self).__init__(
            expression,
            distinct='DISTINCT ' if distinct else '',
            output_field=CharField(),
            **extra)

and use it simply as:

query_set = Fruits.objects.values('type').annotate(count=Count('type'),
                       name = Concat('name')).order_by('-count')

I am using django 1.8 and mysql 4.0.3