old_contents: from django.db import models
  
  class Bill(models.Model):
  
      bill_date = models.DateField()
  
  class Service(models.Model):
  
      reference = models.CharField(max_length=5)
      name = models.CharField(max_length=128)
      description = models.CharField(max_length=1024)
      price = models.FloatField()
  
  class BillLine(models.Model):
  
      bill = models.ForeignKey(Bill)
      service = models.ForeignKey(Service)
      quantity = models.SmallIntegerField(default=1)
      total = models.FloatField()
  
new_contents: from django.db import models
  
  class Bill(models.Model):
  
      bill_date = models.DateField()
  
  class Service(models.Model):
  
      reference = models.CharField(max_length=5)
      name = models.CharField(max_length=128)
      description = models.CharField(max_length=1024)
      price = models.FloatField()
  
      def __unicode__(self):
          """ Return name as object representation """
          return self.name
  
  class BillLine(models.Model):
  
      bill = models.ForeignKey(Bill)
      service = models.ForeignKey(Service)
      quantity = models.SmallIntegerField(default=1)
      total = models.FloatField()
  
subject: add object representation name