HHH-10455 - MapJoin results in NPE when using key()

(cherry picked from commit 6d208331a9)

hibernate-entitymanager/src/main/java/org/hibernate/jpa/criteria/path/MapKeyHelpers.java

@@ -32,6 +32,11 @@ import org.hibernate.persister.collection.CollectionPersister;
  * @author Steve Ebersole
  */
 public class MapKeyHelpers {
+	/**
+	 * Disallow instantiation
+	 */
+	private MapKeyHelpers() {
+	}
 
 	/**
 	 * Models a path to a map key.  This is the actual return used from {@link javax.persistence.criteria.MapJoin#key}
@@ -166,12 +171,11 @@ public class MapKeyHelpers {
 			return mapJoin.getPathIdentifier();
 		}
 
+		@Override
+		public void prepareAlias(RenderingContext renderingContext) {
+			mapJoin.prepareAlias( renderingContext );
 		}
 
-	/**
-	 * Disallow instantiation
-	 */
-	private MapKeyHelpers() {
 	}
 
 	/**

hibernate-entitymanager/src/test/java/org/hibernate/jpa/test/criteria/mapjoin/MapJoinTest2.java

@@ -0,0 +1,110 @@
+/*
+ * 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.jpa.test.criteria.mapjoin;
+
+import java.io.Serializable;
+import java.util.HashMap;
+import java.util.Map;
+import javax.persistence.CollectionTable;
+import javax.persistence.Column;
+import javax.persistence.ElementCollection;
+import javax.persistence.Embeddable;
+import javax.persistence.Entity;
+import javax.persistence.EntityManager;
+import javax.persistence.EnumType;
+import javax.persistence.Enumerated;
+import javax.persistence.GeneratedValue;
+import javax.persistence.Id;
+import javax.persistence.JoinColumn;
+import javax.persistence.MapKeyJoinColumn;
+import javax.persistence.SequenceGenerator;
+import javax.persistence.Table;
+import javax.persistence.criteria.CriteriaBuilder;
+import javax.persistence.criteria.CriteriaQuery;
+import javax.persistence.criteria.MapJoin;
+import javax.persistence.criteria.Root;
+
+import org.hibernate.jpa.test.BaseEntityManagerFunctionalTestCase;
+
+import org.hibernate.testing.TestForIssue;
+import org.junit.Test;
+
+/**
+ * @author Steve Ebersole
+ */
+public class MapJoinTest2 extends BaseEntityManagerFunctionalTestCase {
+	@Override
+	protected Class<?>[] getAnnotatedClasses() {
+		return new Class[] {Batch.class, Node.class, BatchNodeMetadata.class};
+	}
+
+	@Test
+	@TestForIssue( jiraKey = "HHH-10455" )
+	public void testSelectingKeyOfMapJoin() {
+		EntityManager em = getOrCreateEntityManager();
+
+		CriteriaBuilder cb = em.getCriteriaBuilder();
+		CriteriaQuery<Node> query = cb.createQuery( Node.class );
+		Root<Batch> root = query.from( Batch.class );
+
+		MapJoin nodes = (MapJoin) root.join( "batchNodeMetadata" );
+
+		query.select( nodes.key() );
+		query.where( cb.equal( root.get( "id" ), 1 ) );
+
+		em.createQuery( query ).getResultList();
+
+		em.close();
+	}
+
+	@Entity
+	@Table(name = "batch")
+	public static class Batch implements Serializable {
+		@Id
+		@GeneratedValue(generator = "BatchGen")
+		@SequenceGenerator(name = "BatchGen", sequenceName = "seq_batch", allocationSize = 1)
+		private Long id;
+
+		@ElementCollection
+		@CollectionTable(
+				name = "batch_node",
+				//uniqueConstraints = @UniqueConstraint(columnNames = {"batch_id", "node_id"}),
+				//foreignKey = @ForeignKey,
+				joinColumns = @JoinColumn(name = "batch_id", nullable = false))
+		@MapKeyJoinColumn(name = "node_id")
+		private Map<Node, BatchNodeMetadata> batchNodeMetadata = new HashMap<>();
+	}
+
+	@Entity
+	@Table(name = "node")
+	public static class Node implements Serializable {
+		@Id
+		@GeneratedValue(generator = "NodeGen")
+		@SequenceGenerator(name = "NodeGen", sequenceName = "seq_node", allocationSize = 1)
+		private Long id;
+	}
+
+	@Embeddable
+	public static class BatchNodeMetadata implements Serializable {
+
+		@Column(nullable = false)
+		@Enumerated(EnumType.STRING)
+		private NodeMigration migrering = NodeMigration.TOTAL;
+
+		public NodeMigration getMigrering() {
+			return migrering;
+		}
+
+		public void setMigrering(NodeMigration migrering) {
+			this.migrering = migrering;
+		}
+	}
+
+	public static enum NodeMigration {
+		TOTAL
+	}
+}