Question

我有这个mixin在视图上应用prefetch_related。这是我应该处理的查询集：

MyMode.objects.all().prefetch_related('projects')

使用这些模型：

class Workspace():
 name = models.CharField(max_length=255)
class Project():
 name = models.CharField(max_length=255)
 workspace = models.Foreignkey(Workspace)

我创建了这个mixin：

class PrefetchRelatedMixin(object):
    prefetch_related = None

    def get_queryset(self):
        if self.prefetch_related is None:
            raise ImproperlyConfigured(u'%(cls)s is missing the prefetch_related'
                "property. This must be a tuple or list." % {
                'cls': self.__class__.__name__})

        if not isinstance(self.prefetch_related, (tuple, list)):
            raise ImproperlyConfigured(u"%(cls)s's select_related property "
                "must be a tuple or list." % {"cls": self.__class__.__name__})

        queryset = super(PrefetchRelatedMixin, self).get_queryset()

        return queryset.prefetch_related(
            ", ".join(self.prefetch_related)
        )

在视图中调用如下：

class WorkspaceView(DetailView):
    prefetch_related = ['projects']
    model = Workspace

    def get_queryset(self):
        return super(WorkspaceView, self).get_queryset()

但是，当我尝试迭代模板中的相关对象时：

{% for p in object.projects %}
    <li>{{ p.name }}</li>
{% empty %}
    <li>No Projects in this Workspace</li>
{% endfor %}

我收到此错误：

'RelatedManager' object is not iterable

mixin中是否有某些东西改变了对象以便它返回一个RelatedManager？

提前致谢！

Answer 1

@danihp拥有它：你需要.all。

此处也有错误：

return queryset.prefetch_related(
            ", ".join(self.prefetch_related)
        )

应该阅读

return queryset.prefetch_related(*self.prefetch_related)

prefetch_related接受多个字符串参数，而不是一个以逗号分隔的字符串。

Answer 2

prefetch_related是RelatedManager，您应该执行获取结果的方法：

在docs示例中：

>>> pizzas = Pizza.objects.prefetch_related('toppings')
>>> [list(pizza.toppings.filter(spicy=True)) for pizza in pizzas]

针对您的情况：

{% for p in object.projects.all %}

通用视图DetailView上的Django prefetch_related

2 个答案: