I am having difficulty serializing a django object.  The problem is that there are foreign keys.  I want the serialization to have data from the referenced object, not just the index.   
For example, I would like the sponsor data field to say "sponsor.last_name, sponsor.first_name" rather than "13".
How can I fix my serialization?
json data:
{"totalCount":"2","activities":[{"pk": 1, "model": "app.activity", "fields": {"activity_date": "2010-12-20", "description": "my activity", "sponsor": 13, "location": 1, .... 
model code:
class Activity(models.Model): 
  activity_date = models.DateField()
  description = models.CharField(max_length=200)
  sponsor = models.ForeignKey(Sponsor)
  location = models.ForeignKey(Location)
class Sponsor(models.Model):
  last_name = models.CharField(max_length=20)
  first_name= models.CharField(max_length=20)
  specialty = models.CharField(max_length=100)
class Location(models.Model):
  location_num = models.IntegerField(primary_key=True)
  location_name = models.CharField(max_length=100)
def activityJSON(request):
    activities = Activity.objects.all()
    total = activities.count()
    activities_json = serializers.serialize("json", activities)
    data = "{\"totalCount\":\"%s\",\"activities\":%s}" % (total, activities_json)
    return HttpResponse(data, mimetype="application/json")