Django--models Many-to-many

Many-to-many--manytomany

Application Scenarios

When you create a row of data in a table, there is a drop-down box with multiple choices (one-to-single box)
For example, to create user information, you need to assign multiple hobbies to the user

Create a table

Either way, one is to use Django to automatically create the third table associated with many-to-many, and the other is to manually create the relational table yourself.

The

Automatically create a third table correspondence for many-to-many tables, based on the code in Django

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class Host(models.Model):    hostname = models.CharField(max_length=32)    port = models.IntegerField()class HostAdmin(models.Model):    username = models.CharField(max_length=32)    email = models.CharField(max_length=32)    host = models.ManyToManyField(Host)

No.2

Custom Many-to-many tables, no ORM are generated by themselves

models.py

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class Host1(models.Model):    hostname = models.CharField(max_length=32)    port = models.IntegerField()class HostAdmin1(models.Model):    username = models.CharField(max_length=32)    email = models.CharField(max_length=32)    host = models.ManyToManyField(Host1, through=‘HostRelation‘)class HostRelation(models.Model):    c1 = models.ForeignKey(Host1)    c2 = models.ForeignKey(HostAdmin1)

view.py

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#多对多自定义创建表    models.HostRelation.objects.create(        c1=models.Host1.objects.get(id=1),        c2=models.HostAdmin1.objects.get(id=2)    )    models.HostRelation.objects.create(        c1_id=2,        c2_id=1    )

Create data

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初始化数据    models.Host.objects.create(hostname=‘c1‘,port=80)    models.Host.objects.create(hostname=‘c2‘,port=80)    models.Host.objects.create(hostname=‘c3‘,port=80)    models.HostAdmin.objects.create(username=‘root‘,email=‘[email protected]‘)    models.HostAdmin.objects.create(username=‘dali‘,email=‘[email protected]‘)    models.HostAdmin.objects.create(username=‘haojie‘,email=‘[email protected]‘)

Add data

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#正向添加    #目的，给大力分配两个主机的管理权限    #1、获取大力用户    admin_obj = models.HostAdmin.objects.get(username=‘dali‘)    #2、获取指定的两个主机    host_list = models.Host.objects.filter(id__lt=3)    #3、将两个主机和大力添加到第三张对应表中    admin_obj.host.add(*host_list)  #反向添加    host_obj = models.Host.objects.get(id=3)    admin_list = models.HostAdmin.objects.filter(id__gt=1)    host_obj.hostadmin_set.add(*admin_list)

Query data?

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#查询数据  #第一种方式    #正向查    admin_obj = models.HostAdmin.objects.all(id=1)    for item in admin_obj:        item.host.all()    #反向查    host_obj = models.Host.objects.get(id=1)    host_obj.hostadmin_set.all()  #第二种方式    relation_list = models.HostRelation.objects.all()    relation_list = models.HostRelation.objects.filter(c2__username=‘dali‘)    for item in relation_list:        print item.c1.hostname        print item.c2.username

From for notes (Wiz)

Django--models Many-to-many