Introducing the Java Datastore API

App Engine for Java includes support for two major standard interfaces for databases: Java Data Objects (JDO) and the Java Persistence API (JPA). Like the other standards-based interfaces in the App Engine Java API, using one of these interfaces makes it easier to move your application from and to another platform. JDO and JPA support different kinds of databases, including object databases and relational databases. They provide an object-oriented interface to your data, even if the underlying database is not an object store.

Many of the concepts of these interfaces translate directly to App Engine datastore concepts: classes are kinds, objects are entities, fields are properties. App Engine’s implementation also supports several advanced features of these interfaces, such as object relationships. Inevitably, some concepts do not translate directly and have behaviors that are specific to App Engine.