(Newbie) Stuck with annotate() docs

[Ankush Thakur]

Folks, I'm having exceptional trouble understanding annotate(), aggregate(), and their various combinations. I'm currently stuck here: https://docs.djangoproject.com/en/1.9/topics/db/aggregation/#combining-multiple-aggregations

The example here uses Book.objects.first().chapters.count(), but there's no chapters model or field at the start of the tutorial. It's frustrating, to say the least. Even if I set up a separate application to test this myself, what do I make of "chapters"? Is it another model with many-to-many relation with Book? When I ran an example with the following models:

class Author(models.Model):

    name = models.CharField(max_length=100)

    age = models.IntegerField()

class Book(models.Model):

    name = models.CharField(max_length=300)

    chapters = models.IntegerField()

    authors = models.ManyToManyField(Author)

I got: 

>>> Book.objects.first().chapters.count()

Traceback (most recent call last):

  File "<console>", line 1, in <module>

AttributeError: 'int' object has no attribute 'count'

>>> 

So basically, I feel like I'm screwed. Please help.

[Tim Graham]

Looks like a typo. Does the rest of the example make sense and work if that line is changed to "Book.objects.first().chapters"?

[Ankush Thakur]

I'm not sure how Book.objects.first().chapters is different from Book.objects.first().chapters.count(), but the point is that "chapters" is not defined in the models at the top of that page! The snippet makes sense if I treat Book.chapters as another ManyToManyField (like authors), but it's really weird to see that error in the docs. So, does that mean I can report it? If yes, to who?

[Tim Graham]

Please give this a try: https://github.com/django/django/pull/6524

[Ankush Thakur]

Yup! Makes sense now. I hope it saves someone some trouble someday. :-)

Thanks a lot, Tim!

Best,

Ankush