Google App Engine and Google Web toolkit<\/p>\n
<\/p>\n
App Engine Datastore – steps on creating JPA objects:<\/p>\n
1) Create JPA Objects with appropriate relationship. The JPA objects require the Key class if you are going to use the JPA relationship to create a relational datastore.<\/p>\n
2) Follow documents in adding test jars for app engine datastore and write test classes. Initialize the \u00a0LocalServiceTestHelper class and then call DAO classes to store and retrieve.<\/p>\n
<\/p>\n
Creating a datastore key: <\/p>\n How to Query Datastore with key:<\/p>\n String modelIdQuery = “Select persitObj from ” + persistObject.getName() + ” persitObj ” try { \/\/ user name query return null;<\/p>\n } <\/p>\n <\/p>\n <\/p>\n
\n
\nKey modelId = KeyFactory.createKey(ModelClass.class.getSimpleName(),
\nsomeModel.getModelLongId());
\n<\/code>
\nMake sure that the Key.toString produces the same string such as ClassSimpleName(1). If the toString does not matches then you do not have the same key.<\/p>\n
\nprotected Object findByKey(Key modelId, Class persistObject) throws Exception {<\/code><\/p>\n
\n+ ” where persitObj.modelId = :modelId “;<\/p>\n
\nvalidateEntityManager();<\/p>\n
\nQuery query = em.createQuery(modelIdQuery);
\nquery.setParameter(“modelId”, modelId);
\nList resultList = query.getResultList();
\n\/\/ lets see if we got a user already in our db.
\nif (resultList.size() > 0) {
\nreturn resultList.get(0);
\n}<\/p>\n
\ncatch (Exception e) {
\nthrow e;
\n}
\n}<\/p>\n