ORM 外键查询

ORM 外键查询

Django 的 ORM 有多种关系：一对一，多对一，多对多。

各自定义的方式为 ：

       一对一： OneToOneField

       多对一： ForeignKey

       多对多： ManyToManyField

from django.db import models

class Engine(models.Model):
    name = models.CharField(max_length=25)

    def __str__(self):         #2.x版本  __unicode__(self)
        return self.name

class Car(models.Model):
    name = models.CharField(max_length=25)
    engine = models.OneToOneField(Engine)

    def __str__(self):
        return self.name

class Engine2(models.Model):
    name = models.CharField(max_length=25)

    def __str__(self):
        return self.name

class Car2(models.Model):
    name = models.CharField(max_length=25)
    engine = models.ForeignKey(Engine2, unique=True)

    def __str__(self):
        return self.name

OneToOneField Example

from testapp.models import Car, Engine
c = Car.objects.get(name='Audi')
e = Engine.objects.get(name='Diesel')
e.car  
# engine 的model 定义中并没有car，这个是自动生成的，用关联表的类名小写直接访问
<Car: Audi>  
# 注意返回内容的不同

ForeignKey with unique=True Example

from testapp.models import Car2, Engine2
c2 = Car2.objects.get(name='Mazda')
e2 = Engine2.objects.get(name='Wankel')
# 在未定义的model中用关联表类名小写加"_set"来访问，多对多也一样
e2.car2_set.all()   
# 注意返回内容的不同，这里是一个QuerySet
[<Car2: Mazda>]   

CODE VIEW

from django.db import models

# Create your models here.

class IDC(models.Model):
    """机房"""
    name = models.CharField(max_length=64, unique=True)

    class Meta:
        verbose_name = '机房'
        verbose_name_plural = "机房"

    def __str__(self):
        return self.name


class Host(models.Model):
    hostname = models.CharField(u'主机名', max_length=64, default="localhost", blank=True, null=True)
    intranet_ipaddr = models.GenericIPAddressField(u'内网地址', unique=True)
    network_ipaddr = models.GenericIPAddressField(u'公网地址', null=True, default=None, blank=True)
    memo = models.TextField(u'备注', blank=True, null=True, default=None)
    status_type = (
        (0, '离线'),
        (1, '在线'),
        (2, '维护中')
    )
    status = models.SmallIntegerField(u'状态', choices=status_type, default=1)
    user = models.ManyToManyField('User', blank=True)
    idc = models.ForeignKey('IDC', blank=True, null=True)
    system_type_choices = ((0, 'Linux'), (1, 'Windows'))
    system_type = models.SmallIntegerField(choices=system_type_choices, default=0)
    enabled = models.BooleanField(default=1, verbose_name="启用本机")

    class Meta:
        verbose_name = '主机'
        verbose_name_plural = "主机"

    def __str__(self):
        return self.hostname


class BusinessUnit(models.Model):
    name = models.CharField(u'业务线', max_length=64, unique=True)
    parent_unit = models.ForeignKey('self', null=True, blank=True)
    memo = models.CharField(u'备注', max_length=128, blank=True)

    class Meta:
        verbose_name = '业务线'
        verbose_name_plural = "业务线"

    def __str__(self):
        return self.name


class User(models.Model):
    username = models.CharField(u'用户名', max_length=64, null=True, blank=True)
    passwd = models.CharField(u'密码', max_length=128, null=True, blank=True)

    class Meta:
        verbose_name = '用户表'
        verbose_name_plural = "用户表"
        unique_together = ("username", 'passwd')

    def __str__(self):
        return self.username

IDC表

from userauth import models
i = models.IDC.objects.get(name="苏州桥机房")

# 反查询，使用小写的表名加_set字段
i.host_set.all()

# 查询结果为QuerySet类型
<QuerySet [<Host: localhost>, <Host: 56.2>]>

Host表

from userauth import models
h = models.Host.objects.get(id=1)

h.hostname
----------'localhost'

 h.intranet_ipaddr
----------'10.10.56.1'

 h.user.all()     # 查询多对多字段
---------<QuerySet [<User: root>, <User: tomcat>]>

 h.idc    # 查询一对多字段
----------<IDC: 苏州桥机房>

User表

from userauth import models
u = models.User.objects.get(username='root')

u.username
---------'root'

 u.passwd
---------'12345678'

 u.host_set.all()     # 反查询多对多字段
--------<QuerySet [<Host: localhost>]>

BusinessUnit表

from userauth import models
b = models.BusinessUnit.objects.all()

b.name
--------'北京'

 b.parent_unit    # 自关联的一对多
-------------<BusinessUnit: 二手车平台>

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