Started a 'Cheat sheet' section in aggregation docs because I desperately need this

       name = models.CharField(max_length=300)

       books = models.ManyToManyField(Book)

Cheat sheet

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In a hurry? Here's how to do common aggregate queries, assuming the models above::

    # Total number of books.

    >>> Book.objects.count()

    2452

    # Total number of books with publisher=BaloneyPress

    >>> Book.objects.filter(publisher__name='BaloneyPress').count()

    73

    # Average price across all books.

    >>> from django.db.models import Avg

    >>> Book.objects.all().aggregate(Avg('price'))

    {'price__avg': 34.35}

    # Max price across all books.

    >>> from django.db.models import Max

    >>> Book.objects.all().aggregate(Max('price'))

    {'price__max': Decimal('81.20')}

    # Each publisher, each with a count of books as a "num_books" attribute.

    >>> from django.db.models import Count

    >>> pubs = Publisher.objects.annotate(num_books=Count('book'))

    >>> pubs

    [<Publisher BaloneyPress>, <Publisher SalamiPress>, ...]

    >>> pubs[0].num_books

    73

    # The top 5 publishers, in order by number of books.

    >>> from django.db.models import Count

    >>> pubs = Publisher.objects.annotate(num_books=Count('book')).order_by('-num_books')[:5]

    >>> pubs[0].num_books

    1323

Generating aggregates over a QuerySet

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