GROUP_CONCAT equivalent in Django
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! =)
Solution 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
Solution 2:
NOTICE that Django (>=1.8) provides Database functions
support.
https://docs.djangoproject.com/en/dev/ref/models/database-functions/#concat
Here is an enhanced version of Shashank Singla
from django.db.models import Aggregate, CharField
class GroupConcat(Aggregate):
function = 'GROUP_CONCAT'
template = '%(function)s(%(distinct)s%(expressions)s%(ordering)s%(separator)s)'
def __init__(self, expression, distinct=False, ordering=None, separator=',', **extra):
super(GroupConcat, self).__init__(
expression,
distinct='DISTINCT ' if distinct else '',
ordering=' ORDER BY %s' % ordering if ordering is not None else '',
separator=' SEPARATOR "%s"' % separator,
output_field=CharField(),
**extra
)
Usage:
LogModel.objects.values('level', 'info').annotate(
count=Count(1), time=GroupConcat('time', ordering='time DESC', separator=' | ')
).order_by('-time', '-count')