Re: fetching data from intermediate many-to-many table

bs = BookSequence.objects.filter(book__pk=1).select_related()

for s in bs:
       print s.sequence.name, s.number_in_sequence

On Sun, May 1, 2011 at 1:30 PM, Alex <4d876b82@gmail.com> wrote:

Hello!
Assume we have the following models:


class Book(models.Model):
   title = models.CharField()
   sequences = models.ManyToManyField(Sequence,
through='BookSequence')

class Sequence(models.Model):
   name = models.CharField(unique=True)

class BookSequence(models.Model):
   class Meta:
       unique_together = ('book', 'sequence')

   book = models.ForeignKey(Book)
   sequence = models.ForeignKey(Sequence, related_name='detail')
   number_in_sequence = models.IntegerField()


...and are trying to select the sequences a concrete book belongs to,
along with the number of this book in the sequence:


def print_book_sequences():
   book = Book.objects.get(pk=1)
   for seq in book.sequences.select_related():
       number_in_sequence = seq.detail.get(book=book,
sequence=seq).seq_number
       print seq.name, number_in_sequence


So, the question is:

Is there any way in django to select sequence name and sequence number
in one sql query?
The code in print_book_sequences results in two sql queries per
sequence, one selecting name and one number.

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