django get elements with biggest qty of content_set - django

Question

I'm trying to do a reverse key query. The query is this: the foo elements that has the biggest quantity of bar.
Foo:
name = models.CharField('name', max_length=255)
Bar:
name = models.CharField('name', max_length=255)
foo = models.ForeignKey(Foo)
foo_1.name = foo1
foo_2.name = foo2
foo_3.name = foo3
bar_1.name = bar1
bar_1.foo = foo1
bar_2.name = bar2
bar_2.foo = foo2
bar_3.name = bar3
bar_3.foo = foo2
bar_4.name = bar4
bar_4.foo = foo3
bar_4.name = bar4
bar_4.foo = foo3
'Foo2' has 2 'bars' and 'foo3' has 2 'bars' while 'foo1' has only one 'bar'
the result i want is a list with the foos with the biggest quantity of bars and the qty of bars like this:
[{'foo': foo2, 'qty_of_bars': 2}, {'foo': foo3, 'qty_of_bars': 3}]
I've tried a lot of things, for example:
foos = Foo.objects.all()
foos_with_biggest_qty_of_bar = foo.annotate(bar_count=Count('bar')).order_by(
'-bar_count').first()
This gives only one foo, the one with the biggest qty of bars, for example 'foo3', but there may be more than one. In the case above there are 2, foo2 and foo3.
I've tried this:
foos_with_biggest_qty_of_bar = foo.annotate(bar_count=Count('bar')).order_by(
'-bar_count').first()
This gives me the biggest qty of bars related to one single foo
biggest_qty_of_bars = bars.objects.filter(foo=foos_with_biggest_qty_of_bar ).count()
foos_with_biggest_qty_of_bars = Foo.objects.all().annotate(total_bars=biggest_qty_of_bars )
This last line didnt work, i got:
'int' object has no attribute 'lookup'
I tried other thing with a for loop(it's terrible, very ugly, sorry guys for this, by it was an attempt on despair, it's driving me crazy):
qyt_of_bars_of_each_foo = Foo.object.values('name').annotate(
count_bar=Count('bar'))
biggest_number = 0
foo_with_biggest_number_of_bar = []
for qty_of_bar_of_foo in qyt_of_bars_of_each_foo :
if qyt_of_bars_of_each_foo ['count_bar'] >= biggest_number :
foo_with_biggest_number_of_bar .append(qty_of_bar_of_foo)
biggest_number = qyt_of_bars_of_each_foo ['count_bar']
Nothing gave me the result I wanted, which is a list with the foos with the biggest quantity of bars and the qty, like I said before. I'm still trying but as I said it's driving me Crazy, i'm stuck on it since yesterday. Any help I would appreciate a lot!!

Answer 1

Have you tried doing an annotation over the entire queryset using Count and then returning the values as a list?
foo_objects = Foo.objects.all().annotate(
qty_of_bars=Count('bar')).order_by('-qty_of_bars').values(
'name', 'qty_of_bars')
This would return a list, e.g.:
[{'name': u'Foo1', 'qty_of_bars': 3}, {'name': u'Foo2', 'qty_of_bars': 2}]
given an app module name of 'foo' and the following fixture data:
[{
"fields": {
"name": "Foo1"
},
"model": "foo.foo",
"pk": 1
}, {
"fields": {
"name": "Foo2"
},
"model": "foo.foo",
"pk": 2
}, {
"fields": {
"foo": 1,
"name": "Bar1-1"
},
"model": "foo.bar",
"pk": 1
}, {
"fields": {
"foo": 1,
"name": "Bar2-1"
},
"model": "foo.bar",
"pk": 2
}, {
"fields": {
"foo": 1,
"name": "Bar3-1"
},
"model": "foo.bar",
"pk": 3
}, {
"fields": {
"foo": 2,
"name": "Bar1-2"
},
"model": "foo.bar",
"pk": 4
}, {
"fields": {
"foo": 2,
"name": "Bar2-2"
},
"model": "foo.bar",
"pk": 5
}]
update
If you're needing to get to values where qt_of_bars is greater than 1, you can easily get to those via a list comprehension, since you can't filter on an annotated field via the ORM:
foo_objects = [{'foo': f, 'qty_of_bars': f.qty_of_bars}
for f in Foo.objects.all().annotate(
qty_of_bars=Count('bar')).order_by(
'-qty_of_bars') if f.qty_of_bars > 1]
[{'foo': <Foo: Foo1>, 'qty_of_bars': 3}, {'foo': <Foo: Foo2>, 'qty_of_bars': 2}]