Hibernate Tips: How to select multiple scalar values in a Criteria Query

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Hibernate Tips is a series of posts in which I describe a quick and easy solution for common Hibernate questions. If you have a question you like me to answer, 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 define the entity attributes which shall 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.

Learn more:

You can not only use the Criteria API to create database queries, you can also write update and delete statements, as I show in this post: Criteria Update/Delete – The easy way to implement bulk operations with JPA2.1.

And if you want to use the Criteria API in your project, you should also have a look at the JPA metamodel. It provides a great way to create queries in a type-safe way. I explain it in detail in this post: Create type-safe queries with the JPA static metamodel.