HHH-11703 - Entity with Natural ID not being cached in the persistenc…

…eContext, causing extra queries

hibernate-core/src/main/java/org/hibernate/type/EntityType.java

@@ -682,7 +682,7 @@ public Object loadByUniqueKey(
 		final SessionFactoryImplementor factory = session.getFactory();
 		UniqueKeyLoadable persister = (UniqueKeyLoadable) factory.getMetamodel().entityPersister( entityName );
 
-		//TODO: implement caching?! proxies?!
+		//TODO: implement 2nd level caching?! natural id caching ?! proxies?!
 
 		EntityUniqueKey euk = new EntityUniqueKey(
 				entityName,
@@ -697,7 +697,14 @@ public Object loadByUniqueKey(
 		Object result = persistenceContext.getEntity( euk );
 		if ( result == null ) {
 			result = persister.loadByUniqueKey( uniqueKeyPropertyName, key, session );
+
+			// If the entity was not in the Persistence Context, but was found now,
+			// add it to the Persistence Context
+			if (result != null) {
+				persistenceContext.addEntity(euk, result);
+			}
 		}
+
 		return result == null ? null : persistenceContext.proxyFor( result );
 	}
 

hibernate-core/src/test/java/org/hibernate/test/uniquekey/NaturalIdCachingTest.java

@@ -0,0 +1,112 @@
+/*
+ * 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.uniquekey;
+
+import java.io.Serializable;
+import javax.persistence.Entity;
+import javax.persistence.FetchType;
+import javax.persistence.Id;
+import javax.persistence.JoinColumn;
+import javax.persistence.JoinColumns;
+import javax.persistence.ManyToOne;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.hibernate.testing.transaction.TransactionUtil.doInHibernate;
+import static org.junit.Assert.assertThat;
+
+import org.hibernate.annotations.NaturalId;
+import org.hibernate.cfg.AvailableSettings;
+import org.hibernate.cfg.Configuration;
+import org.junit.Test;
+import org.hibernate.testing.junit4.BaseCoreFunctionalTestCase;
+
+public class NaturalIdCachingTest extends BaseCoreFunctionalTestCase {
+
+    @Override
+    protected Class[] getAnnotatedClasses() {
+        return new Class[]{
+                PropertyHolder.class,
+                Property.class
+        };
+    }
+
+    @Override
+    protected void configure(Configuration configuration) {
+        super.configure(configuration);
+        configuration.setProperty(AvailableSettings.SHOW_SQL, Boolean.TRUE.toString());
+        configuration.setProperty(AvailableSettings.GENERATE_STATISTICS, "true");
+    }
+
+
+    @Test
+    public void test() throws Exception {
+		doInHibernate( this::sessionFactory, session -> {
+			Property property = new Property( 1, 1, 1 );
+			session.persist( property );
+			session.persist( new PropertyHolder( 1, property ) );
+			session.persist( new PropertyHolder( 2, property ) );
+		} );
+
+        assertThat(sessionFactory().getStatistics().getEntityInsertCount(), is(3L));
+		sessionFactory().getStatistics().clear();
+
+		doInHibernate( this::sessionFactory, session -> {
+			session.byId( PropertyHolder.class ).load( 1 );
+			session.byId( PropertyHolder.class ).load( 2 );
+		} );
+
+		assertThat( sessionFactory().getStatistics().getEntityLoadCount(), is(3L) );
+		assertThat( sessionFactory().getStatistics().getPrepareStatementCount(), is(3L) );
+    }
+
+    @Entity(name = "PropertyHolder")
+	public static class PropertyHolder implements Serializable {
+
+		@Id
+		private Integer id;
+
+		@ManyToOne(fetch = FetchType.LAZY)
+		@JoinColumns({
+			@JoinColumn(name="PROP_CODE", referencedColumnName = "CODE"),
+			@JoinColumn(name="PROP_ITEM", referencedColumnName = "ITEM")
+		})
+		private Property property;
+
+		private String severalOtherFields = "Several other fields ...";
+
+		protected PropertyHolder() {}
+
+		public PropertyHolder(Integer id, Property property) {
+			this.id = id;
+			this.property = property;
+		}
+
+	}
+
+	@Entity(name = "PropertyEntity")
+	public static class Property implements Serializable {
+
+		@Id
+		private Integer id;
+
+		@NaturalId
+		private Integer code;
+
+		@NaturalId
+		private Integer item;
+
+		private String description = "A description ...";
+
+		protected Property(){}
+
+		public Property(Integer id, Integer code, Integer item) {
+			this.id = id;
+			this.code = code;
+			this.item = item;
+		}
+	}
+}