HHH-13095 - Document how to use arithmetic expressions in CASE statements

Author: vladmihalcea

documentation/src/main/asciidoc/userguide/chapters/query/hql/HQL.adoc

@@ -1547,6 +1547,27 @@ include::{sourcedir}/HQLTest.java[tags=hql-searched-case-expressions-example]
 ----
 ====
 
+[[hql-case-arithmetic-expressions]]
+=== CASE expressions with arithmetic operations
+
+If you want to use arithmetic operations in the CASE expressions, you need to wrap the arithmetic operation in parentheses
+as illustrated by the following example:
+
+[[hql-case-arithmetic-expressions-example]]
+.Case expression with arithmetic operation example
+====
+[source, JAVA, indent=0]
+----
+include::{sourcedir}/HQLTest.java[tags=hql-case-arithmetic-expressions-example]
+----
+====
+
+[IMPORTANT]
+====
+Without wrapping the arithmetic expression in `(` and `)`, the entity query parser will not be able to
+parse the arithmetic operators.
+====
+
 [[hql-nullif]]
 === NULLIF expressions
 

documentation/src/test/java/org/hibernate/userguide/hql/HQLTest.java

@@ -1738,6 +1738,28 @@ public void test_searched_case_expressions_example_2() {
 		});
 	}
 
+	@Test
+	public void test_case_arithmetic_expressions_example() {
+		doInJPA( this::entityManagerFactory, entityManager -> {
+			//tag::hql-case-arithmetic-expressions-example[]
+			List<Long> values = entityManager.createQuery(
+				"select " +
+				"	case when p.nickName is null " +
+				"		 then (p.id * 1000) " +
+				"		 else p.id " +
+				"	end " +
+				"from Person p " +
+				"order by p.id", Long.class)
+			.getResultList();
+
+			assertEquals(3, values.size());
+			assertEquals( 1L, (long) values.get( 0 ) );
+			assertEquals( 2000, (long) values.get( 1 ) );
+			assertEquals( 3000, (long) values.get( 2 ) );
+			//end::hql-case-arithmetic-expressions-example[]
+		});
+	}
+
 	@Test
 	public void test_hql_null_if_example_1() {
 		doInJPA( this::entityManagerFactory, entityManager -> {

hibernate-core/src/test/java/org/hibernate/test/hql/CaseStatementTest.java

@@ -6,6 +6,7 @@
  */
 package org.hibernate.test.hql;
 
+import java.util.List;
 import javax.persistence.Entity;
 import javax.persistence.Id;
 
@@ -14,11 +15,14 @@
 import org.hibernate.Transaction;
 import org.hibernate.engine.spi.SessionImplementor;
 
+import org.hibernate.testing.TestForIssue;
 import org.hibernate.testing.junit4.BaseCoreFunctionalTestCase;
 import org.junit.Test;
 
 import static org.hibernate.testing.junit4.ExtraAssertions.assertTyping;
+import static org.hibernate.testing.transaction.TransactionUtil.doInHibernate;
 import static org.hibernate.testing.transaction.TransactionUtil2.inTransaction;
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.fail;
 
 /**
@@ -128,6 +132,29 @@ public void testSearchedCaseStatementFixture() {
 		s.close();
 	}
 
+	@Test
+	@TestForIssue( jiraKey = "HHH-13095" )
+	public void testSearchedCaseStatementArithmeticExpression() {
+		doInHibernate( this::sessionFactory, session -> {
+			Person steve = new Person();
+			steve.id = 1;
+			steve.name = "Steve";
+			session.persist( steve );
+
+			Person brian = new Person();
+			brian.id = 2;
+			brian.name = "Brian";
+			session.persist( brian );
+
+			List<Integer> values = session.createQuery(
+				"select case when p.name = 'Steve' then (p.id * 10) else p.id end from Person p order by p.id" )
+			.getResultList();
+
+			assertEquals( 10, (int) values.get( 0 ) );
+			assertEquals( 2, (int) values.get( 1 ) );
+		} );
+	}
+
 	@Test
 	public void testSearchedCaseStatementWithParamResult() {
 		Session s = openSession();