HHH-10824 - Fix query stream API to support returning R rather than Object[] when selecting one type.

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

@@ -790,7 +790,7 @@ public class HQLTest extends BaseEntityManagerFunctionalTestCase {
 		doInJPA( this::entityManagerFactory, entityManager -> {
 			Session session = entityManager.unwrap( Session.class );
 			//tag::hql-api-stream-example[]
-			Stream<Object[]> persons = session.createQuery(
+			Stream<Person> persons = session.createQuery(
 				"select p " +
 				"from Person p " +
 				"where p.name like :name" )
@@ -798,7 +798,6 @@ public class HQLTest extends BaseEntityManagerFunctionalTestCase {
 			.stream();
 
 			Map<Phone, List<Call>> callRegistry = persons
-				.map( row -> Person.class.cast( row[0] ) )
 				.flatMap( person -> person.getPhones().stream() )
 				.flatMap( phone -> phone.getCalls().stream() )
 				.collect(Collectors.groupingBy(Call::getPhone));

hibernate-core/src/main/java/org/hibernate/internal/AbstractScrollableResults.java

@@ -121,6 +121,11 @@ public abstract class AbstractScrollableResults implements ScrollableResultsImpl
 		return this.closed;
 	}
 
+	@Override
+	public int getNumberOfTypes() {
+		return this.types.length;
+	}
+
 	@Override
 	public final Object[] get() throws HibernateException {
 		if ( closed ) {

hibernate-core/src/main/java/org/hibernate/query/internal/ScrollableResultsIterator.java

@@ -36,6 +36,11 @@ class ScrollableResultsIterator<T> implements CloseableIterator {
 	@Override
 	@SuppressWarnings("unchecked")
 	public T next() {
-		return (T) scrollableResults.get();
+		if ( scrollableResults.getNumberOfTypes() == 1 ) {
+			return (T) scrollableResults.get()[0];
+		}
+		else {
+			return (T) scrollableResults.get();
+		}
 	}
 }

hibernate-core/src/main/java/org/hibernate/query/spi/ScrollableResultsImplementor.java

@@ -17,4 +17,5 @@ import org.hibernate.ScrollableResults;
 @Incubating
 public interface ScrollableResultsImplementor extends ScrollableResults {
 	boolean isClosed();
+	int getNumberOfTypes();
 }

hibernate-core/src/test/java/org/hibernate/test/stream/basic/BasicStreamTest.java

@@ -6,6 +6,7 @@
  */
 package org.hibernate.test.stream.basic;
 
+import java.util.Optional;
 import java.util.stream.Stream;
 import javax.persistence.Entity;
 import javax.persistence.Id;
@@ -15,11 +16,15 @@ import org.hibernate.Session;
 import org.hibernate.boot.MetadataSources;
 import org.hibernate.engine.spi.SessionImplementor;
 
+import org.hibernate.query.Query;
+import org.hibernate.testing.TestForIssue;
 import org.hibernate.testing.junit4.BaseNonConfigCoreFunctionalTestCase;
 import org.junit.Test;
 
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.core.Is.is;
+import static org.hibernate.testing.junit4.ExtraAssertions.assertTyping;
+import static org.junit.Assert.assertNotNull;
 
 /**
  * @author Steve Ebersole
@@ -50,6 +55,45 @@ public class BasicStreamTest extends BaseNonConfigCoreFunctionalTestCase {
 		session.close();
 	}
 
+	@Test
+	@TestForIssue(jiraKey = "HHH-10824")
+	public void testQueryStream() {
+		Session session = openSession();
+		try {
+
+			session.getTransaction().begin();
+			MyEntity e= new MyEntity();
+			e.id = 1;
+			e.name = "Test";
+			session.persist( e );
+			session.getTransaction().commit();
+			session.clear();
+
+			// Test stream query without type.
+			Object result = session.createQuery( "From MyEntity" ).stream().findFirst().orElse( null );
+			assertTyping( MyEntity.class, result );
+
+			// Test stream query with type.
+			result = session.createQuery( "From MyEntity", MyEntity.class ).stream().findFirst().orElse( null );
+			assertTyping( MyEntity.class, result );
+
+			// Test stream query using forEach
+			session.createQuery( "From MyEntity", MyEntity.class ).stream().forEach( i -> {
+				assertTyping( MyEntity.class, i );
+			} );
+
+			Stream<Object[]> data = session.createQuery( "SELECT me.id, me.name FROM MyEntity me" ).stream();
+			data.forEach( i -> {
+				assertTyping( Integer.class, i[0] );
+				assertTyping( String.class, i[1] );
+			});
+
+		}
+		finally {
+			session.close();
+		}
+	}
+
 	@Entity(name = "MyEntity")
 	@Table(name="MyEntity")
 	public static class MyEntity {