django多對多

創建多對多

方式一：自定義關系表

class Host(models.Model):
    id = models.AutoField(primary_key=True)
    hostname = models.CharField(max_length=32)
    ip = models.GenericIPAddressField(protocol='ipv4')
    port = models.IntegerField()
    b = models.ForeignKey(to='Business',to_field='id')

    def __str__(self):
        return self.hostname

class Application(models.Model):
    name = models.CharField(max_length=32)

class HostToApp(models.Model):
    hobj = models.ForeignKey('Host')
    aobj = models.ForeignKey('Application')
    status = models.CharField(max_length=32)

方式二：自動創建表關系

class Host(models.Model):
    id = models.AutoField(primary_key=True)
    hostname = models.CharField(max_length=32)
    ip = models.GenericIPAddressField(protocol='ipv4')
    port = models.IntegerField()
    b = models.ForeignKey(to='Business',to_field='id')

    def __str__(self):
        return self.hostname

class Application(models.Model):
    name = models.CharField(max_length=32)
    r = models.ManyToManyField(to='Host')　　# 這個字段在表里不存在。

無法直接對第三張表操作
obj = Application.objects.get(id=1)
obj.name
# 對第三張表操作
#添加
obj.r.add(1)　　#對第三張表添加application_id=1,host_id=1
obj.r.add(2,3)    #對第三張表添加application_id=1,host_id=2;application_id=1,host_id=3
obj.r.add(*[1,2,3])　　#對第三張表添加application_id=1,host_id=1;application_id=1,host_id=2;application_id=1,host_id=3
#刪除
obj.r.remove(1)     #刪除第三張表application_id=1,host_id=1
obj.r.remove(2,3)    #刪除第三張表application_id=1,host_id=2;application_id=1,host_id=3
obj.r.remove(*[1,2,3]) #刪除第三張表application_id=1,host_id=1;application_id=1,host_id=2;application_id=1,host_id=3

obj.r.clear()    #刪除第三張表的application_id=1的所有數據

#更新
obj.name = 'new_name'
obj.save()
obj.r.set([1,2,3])    #設置第三張表的application_id=1的數據為application_id=1,host_id=1;application_id=1,host_id=2;application_id=1,host_id=3其它數據刪除