Queries in Django Models

Question

I have two models related with ForeignKey and I am using select_related to fetch data from them:

class Translation(models.Model):
    pk_translation = UUIDField(auto=True, primary_key=True, serialize=True, hyphenate=True)
    en = models.TextField('English', blank = True, null = True)
    fr = models.TextField('French',  blank = True, null = True)
    de = models.TextField('German',  blank = True, null = True)
    it = models.TextField('Italian', blank = True, null = True)
    creationLanguage = models.CharField(max_length=3, choices=s.LANGUAGES, blank = True, null = True)

    def __str__(self):             # __unicode__ on Python 2
        if self.creationLanguage is not None:
            return getattr(self, str(self.creationLanguage))
        else:
            return str(self.en)

class Brainframe(models.Model):
    pk_brainframe = UUIDField(auto=True, primary_key=True, serialize=True, hyphenate=True)
    title = models.OneToOneField(Translation, related_name='Brainframe.title')
    description = models.OneToOneField(Translation, related_name='Brainframe.description')

    def __str__(self):              # __unicode__ on Python 2
        return self.title.__str__()

class Adjacency(models.Model):
    pk_adjacency = UUIDField(auto=True, primary_key=True, hyphenate=True)
    fk_brainframe_parent = models.ForeignKey('Brainframe', related_name='Adjacency.parent')
    fk_brainframe_child = models.ForeignKey('Brainframe', related_name='Adjacency.child')

    def __str__(self):              # __unicode__ on Python 2
        return self.fk_brainframe_child.__str__()

My query is as follows:

root_id = Brainframe.objects.select_related('translation').get(pk=brainframe_id)

brainframes = Adjacency.objects.select_related('brainframe').filter(fk_brainframe_parent=root_id)

for brainframe in brainframes:
        print brainframe.fk_brainframe_parent  #it hit the database

Now, as explained in the select_related documentation, it fetches related objects at once and does not hit the database again. But in my case brainframe.fk_brainframe_parent hits the database every time. But it should not as I have fetched data using select_related. So am I doing something wrong here?

Answer 1

You're using the (lowercased) name of the model in your call to select_related. Instead, use the name of the field, e.g. Adjacency.objects.select_related('fk_brainframe_parent').