Django 之 ForeignKey、ManyToMany的访问方式

1、ForeignKey

情况I：

from django.db import models

class Blog(models.Model):
    pass

class Entry(models.Model):
    blog = models.ForeignKey(Blog)

访问方式：

b = Blog.objects.get(id=1)
b.entry_set.all()

情况II：

from django.db import models

class Blog(models.Model):
    pass

class Entry(models.Model):
    blog = models.ForeignKey(
        Blog,
        related_name='entries'
    )

访问方式：

b = Blog.objects.get(id=1)
b.entries.all()

2、ManyToMany

情况I：

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)

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

访问方法：

>>> beatles = Group.objects.create(name="The Beatles")
>>> beatles.members.all()
<QuerySet [<Person: Ringo Starr>]>

>>> ringo = Person.objects.create(name="Ringo Starr")
>>> ringo.group_set.all()
<QuerySet [<Group: The Beatles>]>

情况II：

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, related_name='groups')

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

访问方法：

>>> beatles = Group.objects.create(name="The Beatles")
>>> beatles.members.all()
<QuerySet [<Person: Ringo Starr>]>

>>> ringo = Person.objects.create(name="Ringo Starr")
>>> ringo.groups.all()
<QuerySet [<Group: The Beatles>]>