django 神奇的双下划线，通过外键的三种查询方式

一，用于跨表操作

　　只要是object后面字符串都是用双下划线__。其它地方用点.

如：的values中的group_code__name.group_code是一个外键

def list(request):
    host = models.host.objects.filter(id__gt=3).values('ip','port','group_code_id','group_code__name')
    for i in host:
        print(i['group_code__name'],i['group_code_id'])
    return render(request,'list.html',{'host':host,})　　

二，3种外键查询

veiws:
def list(request):
    v1 = models.host.objects.filter(id__gt=3)
    for i in v1:
        print(i.ip,i.port,i.group_code_id,i.group_code.name)
    v2 = models.host.objects.filter(id__gt=3).values('ip','port','group_code_id','group_code__name')
    for i in v2:
        print(i['ip'],i['port'],i['group_code__name'],i['group_code_id'])
    v3 = models.host.objects.filter(id__gt=3).values_list('ip','port','group_code_id','group_code__name')
    for i in v3:
        print(i[0],i[1],i[2],i[3])
    return render(request,'list.html',{'v1':v1,'v2':v2,'v3':v3})html:
<h1>对象获取：</h1>
<table border="1">
        <thead><td>ip</td><td>port</td><td>group_id</td><td>group_name</td></thead>
    {% for i in v1 %}
        <tr><td>{{ i.ip}}</td><td>{{ i.port}}</td><td>{{ i.group_code_id}}</td><td>{{ i.group_code.name}}</td></tr>
    {% endfor %}
</table>
<h1>字典获取：</h1>
<table border="1">
        <thead><td>ip</td><td>port</td><td>group_id</td><td>group_name</td></thead>
    {% for i in v2 %}
        <tr><td>{{ i.ip}}</td><td>{{ i.port}}</td><td>{{ i.group_code_id}}</td><td>{{ i.group_code__name}}</td></tr>
    {% endfor %}
</table>
<h1>元组获取：</h1>
<table border="1">
        <thead><td>ip</td><td>port</td><td>group_id</td><td>group_name</td></thead>
    {% for i in v3 %}
        <tr><td>{{ i.0}}</td><td>{{ i.1}}</td><td>{{ i.2}}</td><td>{{ i.3}}</td></tr>
    {% endfor %}
</table>

。。