检查Google应用引擎数据存储中是否存在实体。 [英] Checking if Entity exists in google app engine datastore.

问题描述

检查Google-app-engine数据存储中是否存在实体的最佳/最快方法是什么？现在我试图通过键获取实体，并检查get（）是否返回错误。

我不知道获取实体的过程数据存储。有没有更快的方法来做这种检查？ / code>已被弃用，以赞成App Engine GCS客户端。

您是否考虑过使用查询？猜测和检查不是一种可扩展的方式来查找数据存储中存在的实体。可以创建查询以从数据存储中检索符合指定条件的实体：

https://developers.google.com/appengine/docs/java/datastore/queries

编辑：

关键唯一查询怎么样？只有键的查询比返回完整实体的查询运行得更快。只返回键，使用Query.setKeysOnly（）方法。

  new Query（Kind）。addFilter（Entity .KEY_RESERVED_PROPERTY，FilterOperator.EQUAL，key）.setKeysOnly（）; 
  

来源：[1]： http://groups.google.com/group/google-appengine-java/browse_thread/thread/b1d1bb69f0635d46/ 0e2ba938fad3a543？pli = 1

What is the best/fastest way to check if an Entity exists in a google-app-engine datastore? For now I'm trying to get the entity by key and checking if the get() returns an error.

I don't know the process of getting an Entity on the datastore. Is there a faster way for doing only this check?

解决方案

com.google.appengine.api has been deprecated in favor of the App Engine GCS client.

Have you considered using a query? Guess-and-check is not a scalable way to find out of an entity exists in a data store. A query can be created to retrieve entities from the datastore that meet a specified set of conditions:

https://developers.google.com/appengine/docs/java/datastore/queries

EDIT:

What about the key-only query? Key-only queries run faster than queries that return complete entities. To return only the keys, use the Query.setKeysOnly() method.

new Query("Kind").addFilter(Entity.KEY_RESERVED_PROPERTY, FilterOperator.EQUAL, key).setKeysOnly();

Source: [1]: http://groups.google.com/group/google-appengine-java/browse_thread/thread/b1d1bb69f0635d46/0e2ba938fad3a543?pli=1

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