对象化从实体查询属性 [英] Objectify Query a attribute from an entity

问题描述

有没有一种方法可以使用Objectify查询某个实体的特定属性， 可以说我有一个具有属性的类实体{id，name ，邮件} ，如何只从实体过滤邮件属性？先前我正在提取整个实体

  Objectify ofy = ObjectifyService.begin（）; 
查询< entity> Q = ofy.query（entity.class）; 
  

然后检索q.getmail（）;

我正在寻找仅在查询q中过滤来自实体 * 的 * 邮件属性？请让我知道如何做到这一点。 解决方案

用查询加载整个实体作为bean。有没有真正的SQL的同义词从实体选择邮件其中id =？客观化。你可以做的是在你使用LoadGroups（https://code.google.com/p/objectify-appengine/wiki/BasicOperations###########################################################################################） Load_Groups），但我不认为这就是你要求的。

也就是说，获取1个字段并获取整个对象在appengine中花费的时间基本相同。

Is there a possible way to query a particular attribute from an entity using Objectify,

Lets say i have an Class entity with attributes {id,name,mail},how to filter only the mail attribute from the entity ? previously I was fetching the entire entity

Objectify ofy=ObjectifyService.begin();
Query<entity> q=ofy.query(entity.class);

and then retrieving the value q.getmail();

I am looking for filtering only *mail attribute from entity * in the query q ? please let me know how to do it.

解决方案

That's not how objectify works. You load the entire entity as a bean with a query. There's not really a synonym for SQL "select mail from entity where id=?" in objectify. What you can do is control which associated entities in the graphy are loaded from the datastore when you do a fetch (in objectify 4) using LoadGroups (https://code.google.com/p/objectify-appengine/wiki/BasicOperations#Load_Groups) but I don't think that's what you are asking.

That said, fetching 1 field and fetching an entire object take basically the same amount of time in appengine.

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