HHH-12740 : Subselect fetching doesn't work when multiLoad was used

(cherry picked from commit 579ee65fd3)

hibernate-core/src/main/java/org/hibernate/loader/entity/DynamicBatchingEntityLoaderBuilder.java

@@ -434,6 +434,11 @@ public class DynamicBatchingEntityLoaderBuilder extends BatchingEntityLoaderBuil
 			return false;
 		}
 
+		@Override
+		protected boolean isSubselectLoadingEnabled() {
+			return persister.hasSubselectLoadableCollections();
+		}
+
 		public List doEntityBatchFetch(
 				SharedSessionContractImplementor session,
 				QueryParameters queryParameters,

hibernate-core/src/test/java/org/hibernate/test/ops/multiLoad/MultiLoadSubSelectCollectionTest.java

@@ -0,0 +1,202 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
+ */
+package org.hibernate.test.ops.multiLoad;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import javax.persistence.CascadeType;
+import javax.persistence.Entity;
+import javax.persistence.FetchType;
+import javax.persistence.GeneratedValue;
+import javax.persistence.Id;
+import javax.persistence.ManyToOne;
+import javax.persistence.OneToMany;
+import javax.persistence.Table;
+
+import org.hibernate.CacheMode;
+import org.hibernate.Hibernate;
+import org.hibernate.Session;
+import org.hibernate.annotations.BatchSize;
+import org.hibernate.annotations.Fetch;
+import org.hibernate.annotations.FetchMode;
+import org.hibernate.cfg.AvailableSettings;
+import org.hibernate.stat.Statistics;
+
+import org.hibernate.testing.TestForIssue;
+import org.hibernate.testing.junit4.BaseNonConfigCoreFunctionalTestCase;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import static javax.persistence.GenerationType.AUTO;
+import static org.hibernate.testing.transaction.TransactionUtil.doInHibernate;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * @author Steve Ebersole
+ * @author Gail Badner
+ */
+public class MultiLoadSubSelectCollectionTest extends BaseNonConfigCoreFunctionalTestCase {
+	@Override
+	protected Class[] getAnnotatedClasses() {
+		return new Class[] { Parent.class, Child.class };
+	}
+
+	protected void addSettings(Map settings) {
+		settings.put( AvailableSettings.GENERATE_STATISTICS, "true" );
+	}
+
+	@Before
+	public void before() {
+		Session session = sessionFactory().openSession();
+		session.getTransaction().begin();
+		session.setCacheMode( CacheMode.IGNORE );
+		for ( int i = 1; i <= 60; i++ ) {
+			final Parent p = new Parent( i, "Entity #" + i );
+			for ( int j = 0; j < i ; j++ ) {
+				Child child = new Child();
+				child.setParent( p );
+				p.getChildren().add( child );
+			}
+			session.persist( p );
+		}
+		session.getTransaction().commit();
+		session.close();
+	}
+
+	@After
+	public void after() {
+		Session session = sessionFactory().openSession();
+		session.getTransaction().begin();
+		session.createQuery( "delete Child" ).executeUpdate();
+		session.createQuery( "delete Parent" ).executeUpdate();
+		session.getTransaction().commit();
+		session.close();
+	}
+
+	@Test
+	@TestForIssue( jiraKey = "HHH-12740" )
+	public void testSubselect() {
+		doInHibernate(
+				this::sessionFactory, session -> {
+
+
+					List<Parent> list = session.byMultipleIds( Parent.class ).multiLoad( ids(56) );
+					assertEquals( 56, list.size() );
+
+					// None of the collections should be loaded yet
+					for ( Parent p : list ) {
+						assertFalse( Hibernate.isInitialized( list.get( 0 ).children ) );
+					}
+
+					// When the first collection is loaded, the full batch of 50 collections
+					// should be loaded.
+					Hibernate.initialize( list.get( 0 ).children );
+
+					for ( int i = 0 ; i < 50 ; i++ ) {
+						assertTrue( Hibernate.isInitialized( list.get( i ).children ) );
+						assertEquals( i + 1, list.get( i ).children.size() );
+					}
+
+					// The collections for the 51st through 56th entities should still be uninitialized
+					for (int i = 50 ; i < 56 ; i ++ ) {
+						assertFalse( Hibernate.isInitialized( list.get( i ).children ) );
+					}
+
+					// When the 51st collection gets initialized, the remaining collections should
+					// also be initialized.
+					Hibernate.initialize( list.get( 50 ).children );
+
+					for ( int i = 50 ; i < 56 ; i++ ) {
+						assertTrue( Hibernate.isInitialized( list.get( i ).children ) );
+						assertEquals( i + 1, list.get( i ).children.size() );
+					}
+				}
+		);
+	}
+
+	private Integer[] ids(int count) {
+		Integer[] ids = new Integer[count];
+		for ( int i = 1; i <= count; i++ ) {
+			ids[i-1] = i;
+		}
+		return ids;
+	}
+
+	@Entity( name = "Parent" )
+	@Table( name = "Parent" )
+	@BatchSize( size = 15 )
+	public static class Parent {
+		Integer id;
+		String text;
+		private List<Child> children = new ArrayList<>();
+
+		public Parent() {
+		}
+
+		public Parent(Integer id, String text) {
+			this.id = id;
+			this.text = text;
+		}
+
+		@Id
+		public Integer getId() {
+			return id;
+		}
+
+		public void setId(Integer id) {
+			this.id = id;
+		}
+
+		public String getText() {
+			return text;
+		}
+
+		public void setText(String text) {
+			this.text = text;
+		}
+
+		@OneToMany(mappedBy = "parent", fetch = FetchType.LAZY, cascade = CascadeType.PERSIST)
+		@Fetch(FetchMode.SUBSELECT)
+		public List<Child> getChildren() {
+			return children;
+		}
+
+		public void setChildren(List<Child> children) {
+			this.children = children;
+		}
+	}
+
+	@Entity( name = "Child" )
+	public static class Child {
+
+		@Id
+		@GeneratedValue(strategy = AUTO)
+		private int id;
+
+		@ManyToOne(fetch = FetchType.LAZY, optional = true)
+		private Parent parent;
+
+		public Child() {
+		}
+
+		public Parent getParent() {
+			return parent;
+		}
+
+		public void setParent(Parent parent) {
+			this.parent = parent;
+		}
+
+		public int getId() {
+			return id;
+		}
+	}
+}