追溯外键

Question

I have the following tables:

class Person (models.Model):

    GENDER_CHOICES = (
                      ('M', 'Male'),
                      ('F', 'Female'),
                      )

    first_name = models.CharField(max_length=50)
    last_name  = models.CharField(max_length=50)
    gender = models.CharField(max_length = 1, choices=GENDER_CHOICES, default='M')
    age = models.IntegerField()
    photo = models.ImageField(upload_to='uploads/images/runners', blank=True)

    def __unicode__(self):
        return '%s, %s' % (self.last_name, self.first_name)

and

class Runner (models.Model):
    ''' Represents a runner actually in a particular Race '''
    position = models.IntegerField()
    person = models.ForeignKey(Person, related_name="person")
    race = models.ForeignKey(Race)

and

class Race (models.Model):
    '''An instance of an Event. i.e., the race that is happening this year'''
    year = models.IntegerField()
    description = models.TextField()
    event = models.ForeignKey(Event)

    def leaderboard(self):
        '''
        Orders the leaders and returns the entire set
        Args:
        Returns: 
            A list of Runners ordered by position
        '''
        #board = Runner.objects.prefetch_related("person").filter(race=self).order_by('position') 
        board = Runner.objects.prefetch_related("person")
        print "DEBUG: %s" % board.values()
        return board

What I am trying to accomplish is to retrieve and subsequently encode a JSON response that contains a list of Runner instances with the attributes of each corresponding Person instance contained therein.

In the leaderboard method, I have written an example of my Query. Upon executing it, I get the following:

DEBUG: [{'person_id': 1, 'position': 1, 'id': 1, 'race_id': 1}, {'person_id': 2, 'position': 2, 'id': 2, 'race_id': 1}]

What I want that to look like is to have the QuerySet expand (and replace) each 'person_id" field with a Person instance and all the associated attributes of that instance. (ie, first_name, last_name, etc.

Is this possible? I've tried playing around with both prefetch_related() and select_related but to no avail.

As always, any help is much appreciated.

Answer 1

You can get all of the runners in a race by doing:

self.runner_set.select_related('person')

This will contain all of the runners, and will have a JOIN to the person table.

When you use .values() , then it gives you back the foreign key values, which is not what you want.

If you want, you can use the related_name="runners" within your foreign key to Race. Then you'll be able to access it via self.runners...