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 \tString modelIdQuery = \"Select persitObj from \" + persistObject.getName() + \" persitObj \" \ttry { \t \/\/ user name query \t return null;<\/p>\n \t} <\/p>\n <\/p>\n <\/p>\n
\n
\nKey modelId = KeyFactory.createKey(ModelClass.class.getSimpleName(),\u00a0
\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 {<\/p>\n
\n\t + \" where persitObj.modelId = :modelId \";<\/p>\n
\n\t validateEntityManager();<\/p>\n
\n\t Query query = em.createQuery(modelIdQuery);
\n\t query.setParameter(\"modelId\", modelId);
\n\t List resultList = query.getResultList();
\n\t \/\/ lets see if we got a user already in our db.
\n\t if (resultList.size() > 0) {
\n\t\treturn resultList.get(0);
\n\t }<\/p>\n
\n\tcatch (Exception e) {
\n\t throw e;
\n\t}
\n }
\n<\/code><\/p>\n