How to query as GROUP BY in django?

Question

I query a model:

Members.objects.all()

And it returns:

Eric, Salesman, X-Shop
Freddie, Manager, X2-Shop
Teddy, Salesman, X2         


        

Answer 1

The following module allows you to group Django models and still work with a QuerySet in the result: https://github.com/kako-nawao/django-group-by

For example:

from django_group_by import GroupByMixin

class BookQuerySet(QuerySet, GroupByMixin):
    pass

class Book(Model):
    title = TextField(...)
    author = ForeignKey(User, ...)
    shop = ForeignKey(Shop, ...)
    price = DecimalField(...)

---

class GroupedBookListView(PaginationMixin, ListView):
    template_name = 'book/books.html'
    model = Book
    paginate_by = 100

    def get_queryset(self):
        return Book.objects.group_by('title', 'author').annotate(
            shop_count=Count('shop'), price_avg=Avg('price')).order_by(
            'name', 'author').distinct()

    def get_context_data(self, **kwargs):
        return super().get_context_data(total_count=self.get_queryset().count(), **kwargs)

'book/books.html'

{% for book in object_list %}
    

        
{{ book.title }}
        
{{ book.author.last_name }}, {{ book.author.first_name }}
        
{{ book.shop_count }}
        
{{ book.price_avg }}
    
{% endfor %}

The difference to the annotate/aggregate basic Django queries is the use of the attributes of a related field, e.g. book.author.last_name.

If you need the PKs of the instances that have been grouped together, add the following annotation:

.annotate(pks=ArrayAgg('id'))

NOTE: ArrayAgg is a Postgres specific function, available from Django 1.9 onwards: https://docs.djangoproject.com/en/1.10/ref/contrib/postgres/aggregates/#arrayagg