Django 代理模型和外键 [英] Django proxy model and ForeignKey

问题描述

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

How to make entry.category to be instance of CategoryProxy? See code for details:

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 到 CategoryProxy 的转换也可以，但我对 ORM 内部结构不太熟悉以正确复制内部状态...

Cast from Category to CategoryProxy is ok too, but I am not very familiar with ORM internals to properly copy internal state...

编辑.原因:我给CategoryProxy加了方法，想用他:

EDIT. Reason: I added method to CategoryProxy and want to use him:

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...

but it looks terrible...

推荐答案

从模型类切换到代理类而不访问数据库:

To switch from a model class to a proxy class without hitting the database:

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

上面的代码片段似乎不适用于 django 1.4.

edit: the snippet above seems not working on django 1.4.

从 django 1.4 开始，我像这样手动获取所有值字段:

Since django 1.4, I take all value fields manually like this:

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

从查询集切换到子代理类而不访问数据库:

To switch from a queryset to a child proxy class without hitting database:

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

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