需要在引用属性中按属性排序，有什么好的解决方案? [英] Need to order by properties in the reference property, any good solution?

问题描述

说我有2种:

class Account(db.Model):
  name = db.StringProperty()

  create_time = db.DataTimeProperty()
  last_login = db.DateTimeProperty()
  last_update = db.DataTimeProperty()


class Relationship(db.Model)
  owner = db.ReferenceProperty(Account)
  target = db.ReferenceProperty(Account)
  type = db.IntegerProperty()

我想得到以下查询的等效项:

I want to get the equivalence of following query:

SELECT target 
FROM Relationship
WHERE owner = :key AND type = :type
ORDERBY target.last_login DESC 

该怎么做?

参考: http://www.mail-archive .com/google-appengine @ googlegroups.com/msg15878.html

推荐答案

数据存储区中没有与该查询相当的项目.一些要点:

There's no equivalent for that query in datastore. Some points:

1. 您不能选择一个属性. SELECT始终为SELECT *(您选择整个实体).
2. 您不能加入.您需要对模型进行非规范化以适合您要执行的查询，或者执行多个查询.

1. You can't select a single property. SELECT is always SELECT * (you select a whole entity).
2. You can't do joins. You need to denormalize your models to fit the queries you will perform, or perform multiple queries.

因此，要实现您的目标，您需要将last_login存储在Relationship中，或使用第3个模型作为该特定查询的索引.

So to achieve your goal, you need to have last_login stored in Relationship, or have a 3rd model to serve as index for that specific query.

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