Django use ORM to get range of a particular element - django

Question

I have a model called MyModel which has some dummy data as follows:
item date value
------------------------------
ab 8/10/12 1
ab 7/10/12 2
ab 6/10/12 3
abc 8/10/12 4
abc 7/10/12 5
abc 7/10/12 6
ab 7/10/12 7
ab 7/10/12 8
ab 7/10/12 9
ab 7/10/12 10
abc 7/10/12 11
abc 7/10/12 12
abc 7/10/12 13
I would like to query this Model in such a way that i get an output the gives me the ranges of the items that are in serial, something like the following:
[{'item': 'ab', 'values': '1-3'},
{'item': 'abc', 'values': '4-6'},
{'item': 'ab', 'values': '7-10'},
{'item': 'abc', 'values': '11-13'}]
How would i be able to do this using the django ORM?

Answer 1

Pretty certain you can't do that with the ORM...you'll need to write your own python code to do that.
counts = []
for model in MyModel.objects.all().order_by('value'):
if not counts or last_item != model.item:
counts.append({'item': model.item, 'values': [ model.value ]})
last_item = model.item
elsif model.item == last_item:
counts[-1]['values'].append(model.value)
for count in counts:
count['values'] = '%s-%s' % (count['values'][0], count['values'][-1])
Edit:
counts = []
for model in MyModel.objects.all().order_by('value'):
if not counts or last_item != model.item:
counts.append({'item': model.item, 'first': model.value, 'last':model.value})
last_item = model.item
elsif model.item == last_item:
counts[-1][last] = model.value