blocks|key|1239458|text|JPA是Sun的持久化标准，JDO正在走向死亡(实际上，它已经死亡，但仍在发展)。换句话说，从长远来看，JPA似乎是一项更好的投资。因此，如果两者对我来说都是新的，我想我会选择JPA。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1239459|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

JPA is Sun's standard for persistence, JDO is IMHO dying (actually, it's dead but still moving). In other words, JPA seems to be a better investment on the long term. So I guess I'd choose JPA if both were new to me.

blocks|key|1239513|text|GAE/J+google小组有几篇关于这件事的文章。我会在那里搜索一下，看看人们的意见。你会得到一个与上面表达的观点截然不同的信息。还要关注BigTable不是关系型数据库管理系统这一事实。使用合适的工具来完成工作|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1239514|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

The GAE/J google group has several posts about this very thing. I'd do a search on there and look at people's opinions. You will get a very different message to the opinions expressed above. Also focus on the fact that BigTable is not an RDBMS. Use the right tool for the job

blocks|key|1454494|text|我刚刚通过DataNucleus自己看到了JPA和JDO之间的比较：-+http://www.datanucleus.org/products/accessplatform_2_1/jdo_jpa_faq.html让人大开眼界。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1454495|entityMap|0|LINK|mutability|MUTABLE|url|http://www.datanucleus.org/products/accessplatform_2_1/jdo_jpa_faq.html^0|10|1Z|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

Just saw this comparison between JPA and JDO by DataNucleus themselves:-
<a href="http://www.datanucleus.org/products/accessplatform_2_1/jdo_jpa_faq.html" rel="noreferrer">http://www.datanucleus.org/products/accessplatform_2_1/jdo_jpa_faq.html</a>
An eye-opener.

blocks|key|1239588|text|我是一个快乐的JDO用户。好好干活吧。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1239589|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

I'm a happy user of JDO. Keep up the good work guys.

blocks|key|1454728|text|人们声称JDO已经死了并不是没有价值的。这是我在Pro+EJB+3+Java+Persistence+API一书中读到的内容：“不久之后，Sun宣布JDO将减少到规范维护模式，Java+Persistence+API将从JDO和其他持久性供应商那里汲取经验，并成为未来唯一受支持的标准。”作者Mike+Keith是EJB3的联合规范负责人。当然，他是JPA的坚定支持者，但我怀疑他是否有足够的偏见去撒谎。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1454729|诚然，当这本书出版时，大多数主要供应商都联合起来支持JPA而不是JDO，尽管JDO确实拥有比JPA更高级的技术特性。这并不奇怪，因为EE世界中的大玩家，如IBM/Oracle，也是大型RDBMS供应商。在他们的项目中使用RDMBS的客户比使用非RDMBS的客户多。JDO正在走向死亡，直到GAE给了它一个很大的提振。这是有意义的，因为GAE数据存储不是关系数据库。一些JPA特性不能与bigtable一起工作，比如聚合查询、连接查询、拥有多对多关系。顺便说一句，GAE支持JDO+2.3，但只支持JPA+1.0。如果GAE是您的目标云平台，我将推荐JDO。|1454730|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

People claiming JDO is dead is not without merit. Here is what I read in the book Pro EJB 3 Java Persistence API: "Shortly thereafter Sun announced that JDO would be reduced to specification maintenance mode and that the Java Persistence API would draw from both JDO and the other persistence vendors and become the single supported standard going forward.". The author Mike Keith is the co-specification leader on EJB3. Of course he is a big supporter of JPA, but I doubt he is biased enough to lie. 

It is true that when the book was published, most major vendors were united behind JPA rather than JDO, even though JDO does have more advanced technical features than JPA. It is not surprising because big players in the EE world such as IBM/Oracle are also big RDBMS vendors. More customers are using RDMBS than non-RDMBS in their projects. JDO was dying until GAE gave it a big boost. It makes sense because GAE data store is not relational database. Some JPA features does not work with bigtable such as aggregation queries, Join queries, owned many-to-many relationships. BTW, GAE supports JDO 2.3 while only support JPA 1.0. I will recommend JDO if GAE is your target cloud platform.

blocks|key|1239871|text|在JDO和JPA之间的竞争中，我只能同意datanucleus的帖子。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1239872|首先，也是最重要的，datanucleus的海报知道他们在做什么。毕竟，他们正在开发持久化库，并且熟悉关系以外的数据模型，例如Big+Table。我相信hibernate开发人员一定在这里，他会说：“我们在构建核心库时的所有假设都与关系模型紧密耦合，hibernate并没有针对GAE进行优化。”|1239873|其次，JPA无疑得到了更广泛的使用，成为官方Java+EE堆栈的一部分会有所帮助，但这并不一定意味着它更好。事实上，如果您阅读过JDO，就会发现它对应于比JPA更高的抽象级别。JPA与RDBMS数据模型紧密耦合。|1239874|从编程的角度来看，使用JDO是一个更好的选择，因为您在概念上的妥协要少得多。理论上，只要您使用的提供程序支持底层数据库，您就可以切换到所需的任何数据模型。(在实践中，您很少实现如此高级别的透明性，因为您会发现自己在GAE的对象上设置了主键，并且您会将自己绑定到特定的数据库提供商，例如google)。不过，它仍然会更容易迁移。|1239875|第三，你可以在GAE中使用Hibernate，Eclipse+Link，甚至spring。Google似乎已经做了很大的努力，让你可以使用你用来构建应用程序的框架。但是，当人们构建他们的GAE应用程序时，就好像他们在RDBMS上运行一样，他们意识到它们很慢。GAE上的Spring速度很慢。你可以在谷歌上搜索这个话题的IO视频，看看这是不是真的。|1239876|此外，坚持标准是一件明智的事情，原则上我对此表示赞赏。另一方面，JPA是Java堆栈的一部分，有时会使人们失去选择的概念。如果您愿意，请认识到Java+Server+Faces也是Java+EE堆栈的一部分。对于web+GUI开发来说，它是一个令人难以置信的整洁的解决方案。但最终，为什么人们，如果我可以这么说，更聪明的人，会背离这个标准，转而使用GWT呢？|1239877|在所有这一切中，我必须声明，JPA有一件非常重要的事情要做。这就是Guice及其对JPA的便捷支持。看起来谷歌在这一点上并不像往常那样聪明，目前还不支持JDO。我仍然认为他们负担得起，最终Guice也会吞并JDO，...也可能不是。|1239878|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|S|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|T|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|U|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|V|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|O|$]]

In race between JDO vs JPA I can only agree with the datanucleus posters.

First of all, and also most importantly, the posters of datanucleus know what they are doing. They are after all developing a persistent library and are familiar with data models other than the relational, e.g. Big Table. I am sure that id a developer for hibernate were here, he would have say: "all our assumptions when building our core libraries are tightly coupled to relational model, hibernate is not optimized for GAE".

Secondly, JPA is unquestionably in more widespread use, being a part of the official Java EE stack helps a bit, but that does not necessarily mean that it is better. 
In fact, JDO, if you read about it, corresponds to a higher level of abstraction than JPA. JPA is tightly coupled to the RDBMS data model. 

From a programming stand point, using the JDO APIs is a much better option, because you are conceptually compromising a lot less. You can switch, theoretically to any data model of your desire, provided the provider you use supports the underlying database. 
(In practice you rarely achieve such a high level of transparancy, because you will find yourself setting your primary keys on GAE's object and you will be tying yourself to a specific database provider, e.g. google). it will still be easier to migrate though.

Thirdly, you can use Hibernate, Eclipse Link, and even spring with GAE. Google seems to have made a big effort to allow you to use the frameworks you are used to building your applications on. But what people realize when they build their GAE applications as if they were running on RDBMS is that they are slow. Spring on GAE is SLOW. You can google Google IO videos on this topic to see that it is true.

Also, adhering to standards is a good sensible thing to do, in principle I applaud. On the other hand, JPA being part of the Java EE stack makes people, at times, lose their notion of options. 
Realize, if you will, that Java Server Faces is also part of the Java EE stack. And it is an unbelievably tidy solution for web GUI development. But in the end, why do people, the smarter people if I may say so, deviate from this standard and use GWT instead?

In all of this, I have to sate that there is one very significant thing going for JPA. That is Guice and its convenient support for JPA. Seems that google was not as smart as usual in this point and are content, for now in not supporting JDO. I still think that they can afford it, and eventually Guice will engulf JDO as well,... or maybe not.

blocks|key|1239686|text|使用JDO。即使你没有经验，它也不难掌握，你会有一项新的技能在你的腰带下！|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1239687|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Go JDO. Even if you don't have experience in it, it is not hard to pick up, and you will have a new skill under your belt!

blocks|key|1239721|text|GAE/J计划在年底前添加MYSQL。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1239722|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

GAE/J is slated to add MYSQL before the end of the year.

blocks|key|1454590|text|JPA是未来的发展方向，因为它似乎是一个标准化的API，并且最近在EJB3.0中获得了发展势头。JDO似乎失去了动力。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1454591|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

JPA is the way to go as it seems to be pushed as a standardized API and has recently got momentum in EJB3.0.. JDO seems to have lost the steam.

I want to develop my project on Google App Engine with Struts2. For the database I have two options JPA and JDO. Will you guys please suggest me on it? Both are new for me and I need to learn them. So I will be focused on one after your replies.

Thanks.

JDO vs JPA for Java on Google App Engine

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我想用Struts2在Google App Engine上开发我的项目。对于数据库，我有两个选项: JPA和JDO。你们能给我推荐一下吗？这两个对我来说都是新的，我需要学习它们。因此，我将在您的回复后集中讨论其中一个。谢谢。

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