模型關係
簡介
關係數據庫的威力體現在表之間的相互關聯,Django提供了三種最常見的數據庫關係:多對一(many-to-one),多對多(many-to-many),一對一(one-to-one)
- 多對一關係
- 多對多關係
- 一對一關係
多對一
- django是使用django.db.models.ForeignKey 定義多對一關係
- ForeignKey需要一個位置參數來指定本Model關聯的Model,ForeignKey關聯的Model是"一", ForeignKey所在的Model是"多"
比如汽車和製造商的例子,一輛汽車只能屬於一個製造商,但是一個製造商有多輛汽車,這個關係,用Django的Model來表示,就是
class Manufacturer(models.Model):
name = models.CharField(max_length=30)
class Car(models.Model):
manufacturer = models.ForeignKey(Manufacturer)
name = models.CharField(max_length=30)
數據創建
In [1]: from dashboard.models import Manufacturer,Car
In [2]: m1 = Manufacturer()
In [3]: m1.name = "豐田"
In [4]: m1.save()
In [5]: m2 = Manufacturer()
In [6]: m2.name = "大衆"
In [7]: m2.save()
In [8]: m1
Out[8]: <Manufacturer: Manufacturer object>
In [9]: m2
Out[9]: <Manufacturer: Manufacturer object>
In [10]: c1 = Car()
In [11]: c1.name = "xxx1"
In [12]: m = Manufacturer.objects.get(pk=1)
In [13]: c1.manufacturer = m
In [14]: c1.save()
In [15]: c2 = Car()
In [16]: c2.name = "寶來"
In [17]: m3 = Manufacturer.objects.get(pk=2)
In [18]: c2.manufacturer = m3
In [19]: c2.save()
多對一查詢
- 正向查詢( ForeignKey 所在的模型查詢關聯的模型)
In [22]: xxx1 = Car.objects.get(name="xxx1")
In [23]: xxx1
Out[23]: <Car: Car object>
In [24]: xxx1.manufacturer Out[24]: <Manufacturer: Manufacturer object>
In [25]: xxx1.manufacturer.name Out[25]: '寶馬'
- 反向查詢( ForeignKey 指向的模型查詢ForeignKey 所在的模型)
如果模型有一個ForeignKey,那麼該ForeignKey 所指的模型實例可以通過一個管理器返回前一個有ForeignKey的模型的所有實例。默認情況下,這個管理器的名字爲foo_set,其中foo 是源模型的小寫名稱。該管理器返回的查詢集可以用上一節提到的方式進行過濾和操作。
In [27]: m1 = Manufacturer.objects.get(pk=1)
In [28]: m1.car_set.all()
Out[28]: <QuerySet [<Car: Car object>, <Car: Car object>]>
In [29]: c2 = Car.objects.get(pk=2)
In [30]: c2
Out[30]: <Car: Car object>
In [31]: m1.car_set.add(c2)
In [32]: m1.save() 返回多個car對象
多對多
要實現多對多,就要使用django.db.models.ManyToManyField類,和ForeignKey一樣,它也有一個位置參數,用來指定和它關聯的Model
如果不僅僅需要知道兩個Model之間是多對多的關係,還需要知道這個關係的更多信息,比如Person和Group是多對多的關係,每個person可以在多個group裏,那麼group裏可以有多個person
多對多示例
class Group(models.Model):
#...
class Person(models.Model):
groups = models.ManyToManyField(Group)
建議以被關聯模型名稱的複數形式做爲 ManyToManyField 的名字
在哪個模型中設置 ManyToManyField 並不重要,在兩個模型中任選一個即可——不要在兩個模型中都設置
用戶和組操作實例
In [1]: from django.contrib.auth.models import User,Group
In [2]: g = Group.objects.create(name='test')
In [3]: User.objects.all()
Out[3]: <QuerySet []>
In [4]: u = User()
In [5]: u.username = "wanghui"
In [6]: u.email = "[email protected]"
In [7]: u.password = "123456"
In [8]: u.save()
In [9]: u1 = User.objects.get(pk=1)
In [10]: g1 = Group.objects.get(pk=1)
In [11]: u1.groups #證明manytomany在User表
Out[11]: <django.db.models.fields.related_descriptors.create_forward_many_to_many_manager.<locals>.ManyRelatedManager at 0x7f3dce15ea58>
In [12]: g1.user_set
Out[12]: <django.db.models.fields.related_descriptors.create_forward_many_to_many_manager.<locals>.ManyRelatedManager at 0x7f3dce0ec748>
In [13]: g1.user_set.add(u1)
In [14]: g1.save()
In [15]: u1 = User.objects.get(pk=1)
In [16]: u1.groups.all()
Out[16]: <QuerySet [<Group: test>]>
In [17]: g1 = Group.objects.get(pk=1)
In [18]: g1.user_set.all()
Out[18]: <QuerySet [<User: wanghui>]>
處理關聯對象的其它方法
add(obj1, obj2, ...) #添加一指定的模型對象到關聯的對象集中。
create(**kwargs) #創建一個新的對象,將它保存並放在關聯的對象集中。返回新創建的對象。
remove(obj1, obj2, ...) #從關聯的對象集中刪除指定的模型對象。
clear() #從關聯的對象集中刪除所有的對象。
一對一
一對一是通過django.db.models.OneToOneField來實現的,被關聯的Model會被加上Unique的限制, OneToOneField要一個位置參數,與模型關聯的類
當某個對象想擴展自另一個對象時,最常用的方式就是在這個對象的主鍵上添加一對一關係
接口小練習
需求:
GET:獲取所有用戶組列表
GET:獲取組下的成員列表
GET:獲取用戶的組列表
POST:將用戶添加至指定組
POST:將用戶從指定組中踢出
類視圖如下:
from django.contrib.auth.models import User,Group
from django.core import serializers
from django.http import Http404,QueryDict
class GroupListView(View):
def get(self,request,*args,**kwargs):
queryset = Group.objects.all()
return HttpResponse(serializers.serialize("json",queryset),content_type="application/json")
class GroupMembersView(View):
def get_queryset(self):
groupObj = self.get_group_obj()
return groupObj.user_set.all()
def get_group_obj(self):
try:
groupObj = Group.objects.get(name=self.request.GET.get("name"))
except Group.DoesNotExist:
return Http404
except Group.MultipleObjectsReturned:
return Http404
return groupObj
def get(self,request,*args,**kwargs):
user_queryset = self.get_queryset()
return HttpResponse(serializers.serialize("json",user_queryset),content_type="application/json")
class UserGroupsView(View):
def get_queryset(self):
userObj = self.get_user_obj()
return userObj.groups.all()
def get_user_obj(self):
try:
userObj = User.objects.get(username=self.request.GET.get("name"))
except User.DoesNotExist:
return Http404
except User.MultipleObjectsReturned:
return Http404
return userObj
def get(self,request,*args,**kwargs):
group_queryset = self.get_queryset()
return HttpResponse(serializers.serialize("json",group_queryset),content_type="application/json")
class UserGroupManageView(View):
def get_query(self):
groupObj = self.get_group_obj()
userObj = self.get_user_obj()
def get_group_obj(self):
try:
groupObj = Group.objects.get(name=QueryDict(self.request.body).get("name"))
except Group.DoesNotExist:
return Http404
except Group.MultipleObjectsReturned:
return Http404
return groupObj
return groupObj
def get_user_obj(self):
try:
userObj = User.objects.get(username=QueryDict(self.request.body).get("name"))
except User.DoesNotExist:
return Http404
except User.MultipleObjectsReturned:
return Http404
return userObj
def delete(self,request,*args,**kwargs):
groupObj = self.get_group_obj()
userObj = self.get_user_obj()
groupObj.user_set.remove(userObj)
return HttpResponse()
def put(self,request,*args,**kwargs):
groupObj = self.get_group_obj()
userObj = self.get_user_obj()
groupObj.user_set.add(userObj)
return HttpResponse()
- 路由:
urlpatterns = [
url(r'^grouplist/$',views.GroupListView.as_view()),
url(r'^groupmembers/$',views.GroupMembersView.as_view()),
url(r'^usergroups/$',views.UserGroupsView.as_view()),
url(r'^usergroupmanage/$',views.UserGroupManageView.as_view()),
]