django左加入 [英] django left join

问题描述

我有一些左联接问题..我有以下模型

I have a bit of a left join issue.. I have the following models

class CommandInfo(models.Model):
    server = models.ForeignKey(Server)
    count = models.IntegerField(default=1)
    ts = models.DateTimeField(auto_now=True)

class Server(models.Model):
    name = models.CharField(max_length=100)
    group = models.ForeignKey(ApplicationGroup, blank=True, default=0)
    host = models.CharField(max_length=100)
    ip = models.IPAddressField(db_index=True)
    about = models.TextField()
    firstTS = models.DateTimeField(auto_now_add=True)
    lastTS = models.DateTimeField(auto_now=True)
    processed = models.SmallIntegerField(max_length=1, default=0)

    def __unicode__(self):
        return self.host

我需要获取所有服务器实例，如果有的话，将CommandInfo加入其中.

I need to grab all the server instances and left join the CommandInfo to it if there is one.

现在我正在原始sql中完成

Right now I'm doing it in raw sql

from django.db import connection
cursor = connection.cursor()
cursor.execute("SELECT host,ts,count as host FROM servers_server LEFT JOIN cmds_commandinfo ON server_id=servers_server.id")
servers = cursor.fetchall()

推荐答案

您可以使用以下代码:

s = Server.objects.get(id=1)
cmdinfo = s.commandinfo_set.all()

这将返回所有已将s设置为外键的CommandInfo对象的列表.

Which would return a list of all CommandInfo objects that have s set as the foreign key.

您可以在Django文档中获取更多信息，"

You can get more info at the Django docs, "Following Relationships Backward".

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