DataNucleus（通过jpa和jdo接口访问多中数据源）

DataNucleus主页：http://www.datanucleus.org/index.html

简介：

DataNucleus项目为Java运行环境中的应用数据提供了管理，它提供了标准的接口（JDO, JPA）来访问各种类型的数据库资源，如RDBMS, ODBMS, Map-based, Web-based,
documents, graph-based等等，并且你可以利用同样的API来操作所有你的数据，示图如下：

可见，对于HBase这样的NoSQL数据库也提供了JDO/JPA的接口。

最新版本3.2的信息如下：

January 1st 2013- DataNucleus Access Platform 3.2 ("Copernicus") Milestone 2 is released. DataNucleus Access Platform provides persistence and retrieval of Java objects to/from a wide range of datastores including relational, web-based, map-based, and documents. Version 3.2 Milestone 2 includes the following changes

JDO : ability to mark all classes as detachable, overriding metadata
JDO : add convenience accessor for "detachedState" of an object
JDO : provide access to the native query performed by JDOQL
JPA : add convenience accessor for "detachedState" of an object
JPA : provide access to the native query performed by JPQL
JPA : support surrogate version on a class
JPA : fix to exception throwing when using JTA in a JavaEE environment
JPA : support for JPA2.1 "Generate Schema" feature
JPA : improved logix for finding a persistence-unit with a name, and flag duplicate units with the same name
JPA : default to not add classTransformer in JavaEE environment (so user has to enable it)
Update to JMX beans definitions for compliance
Bundle (repackaged) ASM into datanucleus-core for cleaner usage
Fix missing "PreMainClass" for enhancer so runtime enhancement works
Moved "mapped datastores" code into RDBMS plugin (from datanucleus-core) since only used there
Add pooling for ExecutionContext and ObjectProvider objects for performance.
Fix to persist of N-1 relation with detached owner so we don't get multiple element objects
Fix to ClassLoaderImpl/MetaDataUtils to preserve ordering whilst removing dups
Provide access to native query being invoked by a JDOQL/JPQL query
RDBMS : fix to use of named parameters in range clause of query
RDBMS : add statement batching to shifting process for elements in a List
RDBMS : fix to schema generation when we have "subclass-table" part way down an inheritance tree
MongoDB : improvement for polymorphic queries to make use of discriminator column and handle all in single query
MongoDB : improvement to deletion process to not reload same fields multiple times
HBase : support for Bloom filters, in-memory and various other options (Nicolas Seyvet)
Excel : make "poi-ooxml" dependency optional since not needed with XLS
Various minor bug fixes and improvements

This release is downloadable under an Apache 2 license from the DataNucleus community site.

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DataNucleus（通过jpa和jdo接口访问多中数据源）

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