在order_by（）中使用Django自定义模型方法属性 [英] Using a Django custom model method property in order_by()

问题描述

我正在学习Django，我的一些模型有自定义的方法来以特定方式获取值格式。是否可以使用这些自定义方法之一的值定义为具有order_by（）的模型中的属性？

I'm currently learning Django and some of my models have custom methods to get values formatted in a specific way. Is it possible to use the value of one of these custom methods that I've defined as a property in a model with order_by()?

这是一个示例如何实现财产。

Here is an example that demonstrates how the property is implemented.

class Author(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=40)
    email = models.EmailField(blank=True, verbose_name='e-mail')

    def _get_full_name(self):
        return u'%s %s' % (self.first_name, self.last_name)
    full_name = property(_get_full_name)

    def __unicode__(self):
        return self.full_name

使用这个模型我可以做：

With this model I can do:

>>> Author.objects.all()
[<Author: John Doh>, <Author: Jane Doh>, <Author: Andre Miller>]
>>> Author.objects.order_by('first_name')
[<Author: Andre Miller>, <Author: Jane Doh>, <Author: John Doh>]

但我无法做到：

>>> Author.objects.order_by('full_name')
FieldError: Cannot resolve keyword 'full_name' into field. Choices are: book, email, first_name, id, last_name

什么是正确的使用order_by的方法在这样的自定义属性上？

What would be the correct way to use order_by on a custom property like this?

推荐答案

不，你不能这样做。 order_by 应用于数据库级别，但数据库无法知道您的自定义Python方法。

No, you can't do that. order_by is applied at the database level, but the database can't know anything about your custom Python methods.

您可以使用单独的字段来排序：

You can either use the separate fields to order:

Author.objects.order_by('first_name', 'last_name')

或在Python中执行排序：

or do the ordering in Python:

sorted(Author.objects.all(), key=lambda a: a.full_name)

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