JarCastingSimpleDS provides a simple persistence framework for Google AppEngine that gets as little in the way as possible. It is barely a wrapper around Datastore APIs, providing mapping between Entity and Java classes.
You can explore the details about SimpleDS at our presentation for Codemotion 2012.
There is also a demo application on GitHub.
Features
- Supports Guice, Spring or plain Java configuration.
- Support for embedded classes serialized as properties or in JSON format.
- ==, <, <=, >, <=, IN, != and left like are supported.
- Easy transformations between Java Objects and Datastore Entities.
- Easy support for Cursors.
- Validations of expected ancestors
- Transaction support
- Level 1 and 2 Cache
- Cacheable queries
Examples
This is a brief comparison between SimpleDS and JPA:
// JPA retrieve by key
Model m1 = entityManager.find(Model.class, key);
Model m2 = entityManager.find(Model.class, key2);
// SimpleDS retrieve by key
Model m1 = entityManager.get(key);
Map<Key, Model> l = entityManager.get(key1, key2);
// JPA persist changes
entityManager.merge(m1);
entityManager.persist(m2);
// SimpleDS persist changes
entityManager.put(m1);
entityManager.put(ImmutableList.of(m1, m2));
Model m3 = new Model();
entityManager.put(parentKey, m3);
// JPA remove
Model m1 = entityManager.find(Model.class, key);
entityManager.remove(m1);
// SimpleDS remove
entityManager.remove(ImmutableList.of(key1, key2, key3));
Queries
// JPA
Query query = entityManager.createQuery(
"select m from Model m where m.createdAt<=?1 and m.createdBy=?"
);
query.setParameter(1, new Date());
query.setParameter(2, userKey);
return query.getResultList();
// SimpleDS
return entityManager.createQuery(Model.class)
.lessThan("createdAt", new Date())
.equal("createdBy", userKey)
.asList();
// retrieve just keys
return entityManager.createQuery(Model.class)
.keysOnly()
.asList();
// with limits
return entityManager.createQuery(Model.class)
.withOffset(10)
.withLimit(100)
.asList();