Django:与ManyToManyField一起使用select_related

Question

我有 :

class Award(models.Model) :
    name = models.CharField(max_length=100, db_index=True)

class Alias(models.Model) :
    awards = models.ManyToManyField('Award', through='Achiever')

class Achiever(models.Model):
    award = models.ForeignKey(Award)
    alias = models.ForeignKey(Alias)
    count = models.IntegerField(default=1)

我怎样才能Alias拥有全部achiever_set和awards预先填充的？

>>> db.reset_queries()
>>> Alias.objects.filter(id="450867").select_related("achiever_set__award").get().achiever_set.all()[0].award.name
u'Perma-Peddle'
>>> len(db.connection.queries)
3
>>> db.reset_queries()
>>> Alias.objects.filter(id="450867").select_related("awards").get().awards.all()[0].name
u'Dwarfageddon (10 player)'
>>> len(db.connection.queries)
2

我将需要很多访问别名已经获得的奖项(中间表和奖项本身).我如何批量所有这些？

Answer 1

Django版本1.4及以上版本prefetch_related用于此目的.

该prefetch_related方法类似于select_related,但不进行数据库连接.相反,它执行其他数据库查询并在Python中加入.