Jpql

One common question that you may encounter one day when using object-relational-mapping in your application is how to slim down data that you’re retrieving from the persistence layer down to a specific subset for your use-case in an efficient manner and without using complex additional mapping frameworks. In some situations you might declare lazy loaded fields but another approach that I’d like to share with you here are JPA2 constructor expressions. ...

Today we’re going to take a look at the world of object-relational Mapping and how it is done using the Java Persistence API by creating some basic examples, mapping some relations and querying objects using JPQL or the Criteria API.. Prerequisites Java 6 JDK Maven >= 2 If you’d like to take a look behind the scenes e.g. how entities are mapped in your database you could install a RDBMS of your choice .. or just use Derby/JavaDB that is bundled with the JDK 6 ...