python - Django 代理模型和 ForeignKey

Question

如何让entry.category成为CategoryProxy的实例？详情见代码:

class Category(models.Model): pass

class Entry(models.Model):
    category = models.ForeignKey(Category)

class EntryProxy(Entry):
    class Meta:
        proxy = True

class CategoryProxy(Category):
    class Meta:
        proxy = True

entry = EntryProxy.objects.get(pk=1)
entry.category # !!! I want CategoryProxy instance here

从 Category 转换到 CategoryProxy 也可以，但我不太熟悉 ORM 内部结构以正确复制内部状态...

编辑。原因:我给CategoryProxy添加了方法，想用他:

EntryProxy.objects.get(pk=1).category.method_at_category_proxy()

编辑 2。目前我是这样实现的:

EntryProxy._meta.get_field_by_name('category')[0].rel.to = CategoryProxy

但它看起来很糟糕......

Answer 1

在不访问数据库的情况下从模型类切换到代理类:

class EntryProxy(Entry):
    @property
    def category(self):
        new_inst = EntryProxy()
        new_inst.__dict__ = super(EntryProxy, self).category.__dict__
        return new_inst

编辑:上面的代码片段似乎不适用于 django 1.4。

从 django 1.4 开始，我像这样手动获取所有值字段:

class EntryProxy(Entry):
    @property
    def category(self):
        category = super(EntryProxy, self).category
        new_inst = EntryProxy()
        for attr in [f.attname for f in category.__class__._meta.fields] + ['_state']:
            setattr(new_inst, attr, getattr(category, attr))
        return new_inst

在不访问数据库的情况下从查询集切换到子代理类:

class CategoryProxy(Category):
    @property
    def entry_set(self):
        qs = super(CategoryProxy, self).entry_set
        qs.model = EntryProxy
        return qs