I have these two models:

class CommonVehicle(models.Model):
   year = models.ForeignKey(Year)
   series = models.ForeignKey(Series)
   engine = models.ForeignKey(Engine)
   body_style = models.ForeignKey(BodyStyle)
   ...

class Vehicle(models.Model):    
   objects = VehicleManager()
   stock_number = models.CharField(max_length=6, blank=False)
   vin = models.CharField(max_length=17, blank=False)
   common_vehicle = models.ForeignKey(CommonVehicle)
   ....

What I want to do is to have a count of how many times a given CommonVehicle object is used in the Vehicle class. So far my attempts are giving me one number, which is a total of all the records. How can I have the count being the total appearances for each CommonVehicle