Review
We saw that JPA has its own language for writing queries to the database. The major difference between SQL and JPQL is that JPQL is concerned with entities and their properties, not tables and their columns.
SELECT Query¶
Selecting all films from the database. The returned collection would be a List of Film objects.
String query = "SELECT f FROM Film f";
List<Film> results =
em.createQuery(query, Film.class)
.getResultList();
SELECT Query for Properties¶
Selecting all film titles from the database. The returned collection would be a List of String objects.
String query = "SELECT f.title FROM Film f";
List<String> results =
em.createQuery(query, String.class)
.getResultList();
SELECT Query for Multiple Properties¶
Selecting all film titles and descriptions from the database. The returned collection would be a List of Object[] objects.
String query = "SELECT f.title, f.description FROM Film f";
List<Object[]> results =
em.createQuery(query, Object[].class)
.getResultList();
SELECT with Query Parameters¶
Selecting a single film whose title is ACADEMY DINOSAUR. The returned collection would be a List of Film objects, presumably of length 1.
String query =
"SELECT f FROM Film f WHERE f.title = :title";
List<Film> results =
em.createQuery(queryString, Film.class)
.setParameter("title", "ACADEMY DINOSAUR")
.getResultList();