关系数据库的威力体现在表之间的相互关联,Django提供了三种最常见的数据库关系:多对一 (many-to-one),多对多(many-to-many),一对一(one-to-one)
比如汽车和制造商的例子,一辆汽车只能属于一个制造商,但是一个制造商有多辆汽车,这个关系,用Django的Model来表示,就是
#一
class Manufacturer(models.Model):
name = models.CharField(max_length=30)
#多
class Car(models.Model):
manufacturer = models.ForeignKey(Manufacturer)
name = models.CharField(max_length=30)
car = Car.objects.get(pk=2)
car.manufacturer #返回一条Manufacturer 对象
manufacturer = Manufacturer.objects.get(pk=1)
manufacturer.car_set.all() # 返回多个car对象
class Group(models.Model):
name = CharField(max_length=50)
#...
class Person(models.Model):
name = CharField(max_length=50)
groups = models.ManyToManyField(Group)