django-queryset – Page 10

How to output Django queryset as JSON?

January 6, 2023 by Tarik

You can use JsonResponse with values. Simple example: from django.http import JsonResponse def some_view(request): data = list(SomeModel.objects.values()) # wrap in list(), because QuerySet is not JSON serializable return JsonResponse(data, safe=False) # or JsonResponse({‘data’: data}) Or another approach with Django’s built-in serializers: from django.core import serializers from django.http import HttpResponse def some_view(request): qs = SomeModel.objects.all() qs_json … Read more

Django SUM Query?

January 5, 2023 by Tarik

Update: The following incorporates the ISNULL aspect of the original query: from django.db.models import Sum ModelName.objects.filter(field_name__isnull=True).aggregate(Sum(‘field_name’)) # returns {‘field_name__sum’: 1000} for example You’re looking for the Sum aggregation function, which works as follows: ModelName.objects.aggregate(Sum(‘field_name’)) See: https://docs.djangoproject.com/en/dev/ref/models/querysets/#sum

django filter on the basis of text length

January 1, 2023 by Tarik

For Django >= 1.8 you can use the Length function, which is @Pratyush’s CHAR_LENGTH() under the hood for MySQL, or LENGTH() for some other databases: from django.db.models.functions import Length qs = MyModel.objects.annotate(text_len=Length(‘text_field_name’)).filter( text_len__gt=10)

Getting a count of objects in a queryset in Django

December 31, 2022 by Tarik

To get the number of votes for a specific item, you would use: vote_count = Item.objects.filter(votes__contest=contestA).count() If you wanted a break down of the distribution of votes in a particular contest, I would do something like the following: contest = Contest.objects.get(pk=contest_id) votes = contest.votes_set.select_related() vote_counts = {} for vote in votes: if not vote_counts.has_key(vote.item.id): vote_counts[vote.item.id] … Read more

Get last record in a queryset

December 29, 2022 by Tarik

Django Doc: latest(field_name=None) returns the latest object in the table, by date, using the field_name provided as the date field. This example returns the latest Entry in the table, according to the pub_date field: Entry.objects.latest(‘pub_date’)

Count() vs len() on a Django QuerySet

December 22, 2022 by Tarik

Although the Django docs recommend using count rather than len: Note: Don’t use len() on QuerySets if all you want to do is determine the number of records in the set. It’s much more efficient to handle a count at the database level, using SQL’s SELECT COUNT(*), and Django provides a count() method for precisely … Read more

django – query filter on manytomany is empty

December 22, 2022 by Tarik

print TestModel.objects.filter(manytomany=None)

Get the latest record with filter in Django

December 19, 2022 by Tarik

See the docs from django: https://docs.djangoproject.com/en/dev/ref/models/querysets/#latest You need to specify a field in latest(). eg. obj= Model.objects.filter(testfield=12).latest(‘testfield’) Or if your model’s Meta specifies get_latest_by, you can leave off the field_name argument to earliest() or latest(). Django will use the field specified in get_latest_by by default.

many-to-many in list display django

December 19, 2022 by Tarik

You may not be able to do it directly. From the documentation of list_display ManyToManyField fields aren’t supported, because that would entail executing a separate SQL statement for each row in the table. If you want to do this nonetheless, give your model a custom method, and add that method’s name to list_display. (See below … Read more

Select DISTINCT individual columns in django?

December 16, 2022 by Tarik

One way to get the list of distinct column names from the database is to use distinct() in conjunction with values(). In your case you can do the following to get the names of distinct categories: q = ProductOrder.objects.values(‘Category’).distinct() print q.query # See for yourself. # The query would look something like # SELECT DISTINCT … Read more