Hibernate Tips is a series of posts in which I describe a quick and easy solution for common Hibernate questions. Some of the most popular tips are also available as a book.

If you have a question for a future Hibernate Tips post, please leave a comment below.

Question

How can I select a list of scalar values in a Criteria query?

Solution

The CriteriaQuery interface provides the multiselect() method which allows you to select multiple scalar values. The following code snippet shows an example for such a query.

// Prepare query
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Tuple> q = cb.createTupleQuery();
Root<Author> author = q.from(Author.class);

// Select multiple scalar values
q.multiselect(author.get(Author_.firstName).alias("firstName"), author.get(Author_.lastName).alias("lastName"));

List<Tuple> authorNames = em.createQuery(q).getResultList();

for (Tuple authorName : authorNames) {
log.info(authorName.get("firstName") + " " + authorName.get("lastName"));
}

The multiselect() method expects a List or an array of Selection interfaces, which defines the entity attributes that will be fetched from the database. In this example, I use the JPA metamodel to reference the attributes in a type-safe way. When you execute such a CriteriaQuery, it returns a List of Tuple interface implementations. The Tuple interface provides convenient access to the selected values based on its position or its alias. In the code snippet, I defined an alias for each attribute in the query and use it to get them from the Tuple result.