[Django] #10626: Default model ordering affects annotation query

[Django]

#10626: Default model ordering affects annotation query
--------------------------------------+-------------------------------------
 Reporter:  kmassey                   |       Owner:            
   Status:  new                       |   Milestone:  1.1 beta  
Component:  ORM aggregation           |     Version:  1.1-beta-1
 Keywords:  values annotate ordering  |       Stage:  Unreviewed
Has_patch:  0                         |  
--------------------------------------+-------------------------------------
 Example models without default orderings:
 {{{
 class Author(models.Model):
     id = models.IntegerField(primary_key=True,
          help_text='Uniquely identifies an author.')
     name= models.CharField(max_length=200,
          help_text="Author's first name.")

 class Book(models.Model):
     id = models.IntegerField(primary_key=True,
          help_text='Uniquely identifies a book.')
     title = models.CharField(max_length=200,
          help_text='The title of this book.')
     author = models.ForeignKey(Author, db_column='author_id',
          help_text='The author of this book.')
     price = models.FloatField(
          help_text='Price of the book.')
     inventory = models.IntegerField(
          help_text='Copies of book in the store.')
 }}}

 Use values() and annotate() to determine the number of books at each
 price. This works as I expected:
 {{{
 >>> q = Book.objects.values('price').annotate(Count('price'))
 >>> list(q)
 [{'price': 7.9900000000000002, 'price__count': 2}, {'price':
 9.9900000000000002, 'price__count': 1}]
 }}}

 Now add default orderings to the models:
 {{{
 class Author(models.Model):
     id = models.IntegerField(primary_key=True,
          help_text='Uniquely identifies an author.')
     name= models.CharField(max_length=200,
          help_text="Author's first name.")
     class Meta:
         ordering = ['id']

 class Book(models.Model):
     id = models.IntegerField(primary_key=True,
          help_text='Uniquely identifies a book.')
     title = models.CharField(max_length=200,
          help_text='The title of this book.')
     author = models.ForeignKey(Author, db_column='author_id',
          help_text='The author of this book.')
     price = models.FloatField(
          help_text='Price of the book.')
     inventory = models.IntegerField(
          help_text='Copies of book in the store.')
     class Meta:
         ordering = ['id']
 }}}

 And repeat the query:

 {{{
 >>> q = Book.objects.values('price').annotate(Count('price'))
 >>> list(q)
 [{'price': 9.9900000000000002, 'price__count': 1}, {'price':
 7.9900000000000002, 'price__count': 1}, {'price': 7.9900000000000002,
 'price__count': 1}]
 }}}

 This isn't what I expected. It took me a while to make the connection
 between the model default ordering and the behavior of the annotation
 query. Once I saw it, the fix was easy:
 {{{
 >>> q = Book.objects.values('price').annotate(Count('price')).order_by()
 >>> list(q)
 [{'price': 7.9900000000000002, 'price__count': 2}, {'price':
 9.9900000000000002, 'price__count': 1}]
 }}}

 I'm not sure if this should be a bug per se. If not, perhaps it could be
 noted in the aggregation documentation.

 Thanks,
 Kevin

-- 
Ticket URL: <http://code.djangoproject.com/ticket/10626>
Django <http://code.djangoproject.com/>
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