django 1.8文档代码

模型

中介模型

from django.db import models

class Person(models.Model):
name = models.CharField(max_length=128)

def __str__(self):              # __unicode__ on Python 2
return self.name

class Group(models.Model):
name = models.CharField(max_length=128)
members = models.ManyToManyField(Person, through='Membership')

def __str__(self):              # __unicode__ on Python 2
return self.name

class Membership(models.Model):
person = models.ForeignKey(Person)
group = models.ForeignKey(Group)
date_joined = models.DateField()
invite_reason = models.CharField(max_length=64)

shell 操作

>>> ringo = Person.objects.create(name="Ringo Starr")
>>> paul = Person.objects.create(name="Paul McCartney")
>>> beatles = Group.objects.create(name="The Beatles")
>>> m1 = Membership(person=ringo, group=beatles,
...     date_joined=date(1962, 8, 16),
...     invite_reason="Needed a new drummer.")
>>> m1.save()
>>> beatles.members.all()
[<Person: Ringo Starr>]
>>> ringo.group_set.all()
[<Group: The Beatles>]
>>> m2 = Membership.objects.create(person=paul, group=beatles,
...     date_joined=date(1960, 8, 1),
...     invite_reason="Wanted to form a band.")
>>> beatles.members.all()
[<Person: Ringo Starr>, <Person: Paul McCartney>]

查询

通过创建中介模型的实例来建立对多对多关系后，你就可以执行查询了。 和普通的多对多字段一样，你可以直接使用被关联模型的属性进行查询：

# Find all the groups with a member whose name starts with 'Paul'
>>> Group.objects.filter(members__name__startswith='Paul')
[<Group: The Beatles>]

如果你使用了中介模型，你也可以利用中介模型的属性进行查询：

# Find all the members of the Beatles that joined after 1 Jan 1961
>>> Person.objects.filter(
...     group__name='The Beatles',
...     membership__date_joined__gt=date(1961,1,1))
[<Person: Ringo Starr]

如果你需要访问一个成员的信息，你可以直接获取Membership模型：

>>> ringos_membership = Membership.objects.get(group=beatles, person=ringo)
>>> ringos_membership.date_joined
datetime.date(1962, 8, 16)
>>> ringos_membership.invite_reason
'Needed a new drummer.'

另一种获取相同信息的方法是，在Person对象上查询多对多反转关系：

>>> ringos_membership = ringo.membership_set.get(group=beatles)
>>> ringos_membership.date_joined
datetime.date(1962, 8, 16)
>>> ringos_membership.invite_reason
'Needed a new drummer.'

模型的方法

from django.db import models

class Person(models.Model):
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)
birth_date = models.DateField()

def baby_boomer_status(self):
"Returns the person's baby-boomer status."
import datetime
if self.birth_date < datetime.date(1945, 8, 1):
return "Pre-boomer"
elif self.birth_date < datetime.date(1965, 1, 1):
return "Baby boomer"
else:
return "Post-boomer"

def _get_full_name(self):
"Returns the person's full name."
return '%s %s' % (self.first_name, self.last_name)
full_name = property(_get_full_name)

重写预定义的模型方法

from django.db import models

class Blog(models.Model):
name = models.CharField(max_length=100)
tagline = models.TextField()

def save(self, *args, **kwargs):
do_something()
super(Blog, self).save(*args, **kwargs) # Call the "real" save() method.
do_something_else()

阻止保存

from django.db import models

class Blog(models.Model):
name = models.CharField(max_length=100)
tagline = models.TextField()

def save(self, *args, **kwargs):
if self.name == "Yoko Ono's blog":
return # Yoko shall never have her own blog!
else:
super(Blog, self).save(*args, **kwargs) # Call the "real" save() method.