HHH-6598 - Immutable entities should not have up-to-date checks performed on a flush

hibernate-core/src/main/java/org/hibernate/event/internal/DefaultFlushEntityEventListener.java

@@ -120,6 +120,12 @@ public void onFlushEntity(FlushEntityEvent event) throws HibernateException {
 		final var entry = event.getEntityEntry();
 		final var session = event.getSession();
 
+		// short-circuit for immutable entities....
+		if ( !entry.getPersister().isMutable() && !entry.getPersister().hasCollections() ) {
+			// nothing to do
+			return;
+		}
+
 		final boolean mightBeDirty = entry.requiresDirtyCheck( entity );
 
 		final Object[] values = getValues( entity, entry, mightBeDirty, session );

hibernate-core/src/test/java/org/hibernate/orm/test/immutable/ImmutableDirtinessCheckingTests.java

@@ -0,0 +1,88 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.orm.test.immutable;
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.Table;
+import org.hibernate.annotations.Immutable;
+import org.hibernate.testing.orm.junit.DomainModel;
+import org.hibernate.testing.orm.junit.SessionFactory;
+import org.hibernate.testing.orm.junit.SessionFactoryScope;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Steve Ebersole
+ */
+@DomainModel(annotatedClasses = ImmutableDirtinessCheckingTests.ReferenceData.class)
+@SessionFactory
+public class ImmutableDirtinessCheckingTests {
+	@Test
+	void testDirtyCheckingBehavior(SessionFactoryScope factoryScope) {
+		factoryScope.inTransaction( (session) -> {
+			var data = session.find( ReferenceData.class, 1 );
+			data.setName( "another value" );
+			nameAccessCount = 0;
+			session.flush();
+			assertThat( nameAccessCount ).isEqualTo( 0 );
+		} );
+
+		factoryScope.inTransaction( (session) -> {
+			var data = session.find( ReferenceData.class, 1 );
+			assertThat( data.getName() ).isEqualTo( "initial value" );
+		} );
+	}
+
+	@BeforeEach
+	void prepareTestData(SessionFactoryScope factoryScope) {
+		factoryScope.inTransaction( (session) -> {
+			session.persist( new ReferenceData( 1, "initial value" ) );
+		} );
+	}
+
+	@Test
+	void dropTestData(SessionFactoryScope factoryScope) {
+		factoryScope.dropData();
+	}
+
+	private static int nameAccessCount = 0;
+
+	@Entity(name="ReferenceData")
+	@Table(name="ReferenceData")
+	@Immutable
+	public static class ReferenceData {
+		private Integer id;
+		private String name;
+
+		public ReferenceData() {
+		}
+
+		public ReferenceData(Integer id, String name) {
+			this.id = id;
+			this.name = name;
+		}
+
+		@Id
+		public Integer getId() {
+			return id;
+		}
+
+		public void setId(Integer id) {
+			this.id = id;
+		}
+
+		public String getName() {
+			nameAccessCount++;
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+	}
+}