创建模型
在本例中,Place
和 Restaurant 为一对一关系
from django.db import models class Place(models.Model): name = models.CharField(max_length=50) address = models.CharField(max_length=80) def __str__(self): return "%s the place" % self.name class Restaurant(models.Model): place = models.OneToOneField( Place, on_delete=models.CASCADE, primary_key=True, ) serves_hot_dogs = models.BooleanField(default=False) serves_pizza = models.BooleanField(default=False) def __str__(self): return "%s the restaurant" % self.place.name class Waiter(models.Model): restaurant = models.ForeignKey(Restaurant, on_delete=models.CASCADE) name = models.CharField(max_length=50) def __str__(self): return "%s the waiter at %s" % (self.name, self.restaurant)
数据迁移
#生成迁移文件,记录下在models.py文件中的改动 python manage.py makemigrations ##将改动的内容作用于数据库,生成相应的数据 python manage.py migrate
表操作
创建数据
>>> #创建几个地点 >>> p1 = Place(name='Demon Dogs', address='944 W. Fullerton') >>> p1.save() >>> p2 = Place(name='Ace Hardware', address='1013 N. Ashland') >>> p2.save() >>> #创建一家餐厅 >>>r=Restaurant(place=p1,serves_hot_dogs=True, serves_pizza=False) >>> r.save() >>>#Restaurant 可以访问 Place >>> r.place <Place: Demon Dogs the place> >>>#Place 可以访问 Restaurant >>> p1.restaurant <Restaurant: Demon Dogs the restaurant> >>>#P2没有关联餐厅 可以通过捕获异常,避免出错 >>> from django.core.exceptions import ObjectDoesNotExist >>> try: >>> p2.restaurant >>> except ObjectDoesNotExist: >>> print("There is no restaurant here.") There is no restaurant here. >>>#也可以通过 hasattr() 获取是否有某个属性来判断 >>> hasattr(p2, 'restaurant') False >>>#使用赋值符号设置place 。因为Place是restaurant的主键,所以保存将创建一个新的restaurant,将之前的restaurant >>> r.place = p2 >>> r.save() >>> p2.restaurant <Restaurant: Ace Hardware the restaurant> >>> r.place <Place: Ace Hardware the place> >>>#再次设置place,在反向使用赋值: >>> p1.restaurant = r >>> p1.restaurant <Restaurant: Demon Dogs the restaurant>
查询数据
>>>#all()只返回餐馆,而不是地方。注意有两个餐馆, Ace硬件餐厅是在对r.place=p2的调用中创建的 >>> Restaurant.objects.all() <QuerySet [<Restaurant: Demon Dogs the restaurant>, <Restaurant: Ace Hardware the restaurant>]> >>>#all()返回所有位置,不管它们是否有餐馆 >>> Place.objects.order_by('name') <QuerySet [<Place: Ace Hardware the place>, <Place: Demon Dogs the place>]> >>>#可以使用跨关系查找 >>> Restaurant.objects.get(place=p1) <Restaurant: Demon Dogs the restaurant> >>> Restaurant.objects.get(place__pk=1) <Restaurant: Demon Dogs the restaurant> >>> Restaurant.objects.filter(place__name__startswith="Demon") <QuerySet [<Restaurant: Demon Dogs the restaurant>]> >>> Restaurant.objects.exclude(place__address__contains="Ashland") <QuerySet [<Restaurant: Demon Dogs the restaurant>]> >>>#反向查找也是可以的 >>> Place.objects.get(pk=1) <Place: Demon Dogs the place> >>> Place.objects.get(restaurant__place=p1) <Place: Demon Dogs the place> >>> Place.objects.get(restaurant=r) <Place: Demon Dogs the place> >>> Place.objects.get(restaurant__place__name__startswith="Demon") <Place: Demon Dogs the place> >>>#在餐厅里加一个waiter >>> w = r.waiter_set.create(name='Joe') >>> w <Waiter: Joe the waiter at Demon Dogs the restaurant> >>>#访问服务员 >>> Waiter.objects.filter(restaurant__place=p1) <QuerySet [<Waiter: Joe the waiter at Demon Dogs the restaurant>]> >>> Waiter.objects.filter(restaurant__place__name__startswith="Demon") <QuerySet [<Waiter: Joe the waiter at Demon Dogs the restaurant>]>