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>]>