Some JPA Query API code snippet samples

jpa-qry-api-examples.java

	public void findindAllUsingJpqlQuery() throws Exception {
		// given
		String fetchingAllInJpql = "select e from " + ENTITY_NAME
				+ " e order by e.id";

		// when
		System.out.println("Selecting (using JPQL)...");
		List<Entity> entities = em.createQuery(fetchingAllInJpql,
				Entity.class).getResultList();

		// then
		System.out.println("Found " + entities.size()
				+ " entities (using JPQL):");
	}

	public void findAllUsingCriteriaApi() throws Exception {
		// given
		CriteriaBuilder builder = em.getCriteriaBuilder();

		CriteriaQuery<Entity> criteria = builder
				.createQuery(Entity.class);

		Root<Entity> entity = criteria.from(Entity.class);
		criteria.select(entity);
		// TIP: If you don't want to use the JPA 2 Metamodel,
		// you can change the get() method call to get("id")
		criteria.orderBy(builder.asc(entity.get(Entity_.id)));
		// No WHERE clause, which implies select all

		// when
		System.out.println("Selecting (using Criteria)...");
		List<Entity> entities = em.createQuery(criteria).getResultList();

		// then
		System.out.println("Found " + entities.size()
				+ " entities (using Criteria):");
	}
	

	public void findUsingCriteriaApiWhere() throws Exception{
		
		// given
		CriteriaBuilder builder = em.getCriteriaBuilder();

		CriteriaQuery<Entity> criteria = builder
				.createQuery(Entity.class);

		Root<Entity> entity = criteria.from(Entity.class);
		criteria.where(builder.equal(entity.get(Entity_.id), id));

		Entity entity = em.createQuery(criteria).getSingleResult();
	}