google app engine - Why Objectify instead of JDO? -

i approaching gwt + gae world.

my essential need send on gwt-rpc wire entity classes, without duplicating them dtos.

objectify promise pretty well. claims hide "jdo complexity".

i never worked jpa or jdo technologies. where's complexity?

i mean, can provide me simple examples complex tasks in jdo, made trivial objectify?

maybe relationships?

i think jdo/jpa easy play on "hello world" level. changes need more real such composite keys, multiply relationships between entities , etc. jdo gae implementation quite complex , hard grasp beginners, partly due unsupported features, workarounds , extensions. jdo designed work "everywhere", means highly abstracted , general in nature. great portability, means might not perfect match specific engine gae quite unique datastore. datanucleus/jdo/jpa jars quite big (~2.3 mb in total), while objectify's jar pretty small. jdo/jpa might perform class path scanning @ startup find , register entities, add load time. time spent proportional number of classes in project.

as per example think in terms of amount of code jdo/jpa sample will appear simpler lots of dao classes objectify, in general, maintenance of objectify code easier engineer because don't need walk through minefield thinking can break in jdo :)