Django 模型中的查询

Question

我有两个与 ForeignKey 相关的模型，我正在使用 select_related 从它们获取数据：

class Translation(models.Model):
    pk_translation = UUIDField(auto=True, primary_key=True, serialize=True, hyphenate=True)
    en = models.TextField('English', blank = True, null = True)
    fr = models.TextField('French',  blank = True, null = True)
    de = models.TextField('German',  blank = True, null = True)
    it = models.TextField('Italian', blank = True, null = True)
    creationLanguage = models.CharField(max_length=3, choices=s.LANGUAGES, blank = True, null = True)

    def __str__(self):             # __unicode__ on Python 2
        if self.creationLanguage is not None:
            return getattr(self, str(self.creationLanguage))
        else:
            return str(self.en)

class Brainframe(models.Model):
    pk_brainframe = UUIDField(auto=True, primary_key=True, serialize=True, hyphenate=True)
    title = models.OneToOneField(Translation, related_name='Brainframe.title')
    description = models.OneToOneField(Translation, related_name='Brainframe.description')

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

class Adjacency(models.Model):
    pk_adjacency = UUIDField(auto=True, primary_key=True, hyphenate=True)
    fk_brainframe_parent = models.ForeignKey('Brainframe', related_name='Adjacency.parent')
    fk_brainframe_child = models.ForeignKey('Brainframe', related_name='Adjacency.child')

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

我的查询如下：

root_id = Brainframe.objects.select_related('translation').get(pk=brainframe_id)

brainframes = Adjacency.objects.select_related('brainframe').filter(fk_brainframe_parent=root_id)

for brainframe in brainframes:
        print brainframe.fk_brainframe_parent  #it hit the database

现在，如 select_related 文档中所述，它会立即获取相关对象，不会再次访问数据库。但在我的例子中 brainframe.fk_brainframe_parent 每次都会访问数据库。但它不应该，因为我已经使用 select_related 获取了数据。那我是不是做错了什么？

Answer 1

您在调用 select_related 时使用了模型的（小写）名称。相反，使用字段的名称，例如Adjacency.objects.select_related('fk_brainframe_parent').

Django 模型中的查询

Queries in Django Models

python

django

django-models

django-queryset