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Java 构建基于 Google AppEngine 的 Blog

twig-persist

Twig - Making the Datastore more manageableTwig is an object persistence interface built on Google App Engine's low-level datastore which overcomes many of JDO-GAEs limitations including full support for inheritance, polymorphism and generic types. You can easily configure, modify or extend ... [More] Twigs behaviour by implementing your own strategies or overriding extension points in pure Java code. Twig is the only datastore interface to support: Parallel Asynchronous Commands Plain old Java object data models with no datastore dependencies Merged OR queries on multiple properties Read the documentation to get started Visit the Twig Discussion Group Show me some codeThe central interface you will use is ObjectDatastore which has an implementation AnnotationTypesafeDatastore // stateful session configured with annotations ObjectDatastore datastore = new AnnotationObjectDatastore(); // create a complex object graph Band ledzep = createClassicRockband(); // store the instance and all other reachable instances Key key = datastore.store(ledzep); // converted into a query by kind with a key name Band result = datastore.find(Band.class, "Led Zeppelin"); // the identical instance is always returned from same datastore assert result == ledzep; // modernize the classic rock band ledzep.name = "White Stripes"; // call update on changed instances datastore.update(ledzep); // no need to deal with Keys datastore.delete(ledzep); // run a find command Iterator punkBands = datastore.find() .type(Band.class) .addFilter("genre", EQUAL, Genre.PUNK) .returnResultsNow(); A common sentimentA message from the App Engine Java group: "It seems alarming to me that these basic relations are difficult to code. Lets face it, applications are full of these relations...it seems to me that too much developer time is required in the Persistence layer of GAE apps. The Persistence and Presentation layers needs to be a "no brainer", so more focus can be where it needs to be - the business layer. Does anyone feel the same?" - Diana Cruise Twig is named after the super thin sixties model Twiggy - or it could be something like Typesafe Wrapper in GAE [Less]