HHH-19688 @IdClass with single @Id @OneToOne field

hibernate-core/src/main/java/org/hibernate/boot/model/internal/EntityBinder.java

@@ -630,6 +630,11 @@ private static PropertyData getUniqueIdPropertyFromBaseClass(
 		return baseClassElements.get( 0 );
 	}
 
+	/**
+	 * Given the id class of the current entity, as specified by an
+	 * {@link IdClass} annotation, determine if it's actually the
+	 * identifier type or {@link IdClass} of some associated entity.
+	 */
 	private boolean isIdClassPrimaryKeyOfAssociatedEntity(
 			ElementsToProcess elementsToProcess,
 			ClassDetails compositeClass,
@@ -639,26 +644,58 @@ private boolean isIdClassPrimaryKeyOfAssociatedEntity(
 			Map<ClassDetails, InheritanceState> inheritanceStates,
 			MetadataBuildingContext context) {
 		if ( elementsToProcess.getIdPropertyCount() == 1 ) {
+			// There's only one @Id field, so it might be the @EmbeddedId of an associated
+			// entity referenced via a @ManyToOne or @OneToOne association
 			final PropertyData idPropertyOnBaseClass =
 					getUniqueIdPropertyFromBaseClass( inferredData, baseInferredData, propertyAccessor, context );
-			final InheritanceState state =
-					inheritanceStates.get( idPropertyOnBaseClass.getClassOrElementType().determineRawClass() );
+			final TypeDetails idPropertyType = idPropertyOnBaseClass.getClassOrElementType();
+			final InheritanceState state = inheritanceStates.get( idPropertyType.determineRawClass() );
 			if ( state == null ) {
-				return false; //while it is likely a user error, let's consider it is something that might happen
-			}
-			final ClassDetails associatedClassWithIdClass = state.getClassWithIdClass( true );
-			if ( associatedClassWithIdClass == null ) {
-				//we cannot know for sure here unless we try and find the @EmbeddedId
-				//Let's not do this thorough checking but do some extra validation
-				return hasToOneAnnotation( idPropertyOnBaseClass.getAttributeMember() );
-
+				// Likely a user error, but treat it as something that might happen
+				return false;
 			}
 			else {
-				final IdClass idClass = associatedClassWithIdClass.getAnnotationUsage( IdClass.class, modelsContext() );
-				return compositeClass.getName().equals( idClass.value().getName() );
+				final ClassDetails associatedClassWithIdClass = state.getClassWithIdClass( true );
+				if ( associatedClassWithIdClass == null ) {
+					// If annotated @OneToOne or @ManyToOne, it's an association to another entity
+					return hasToOneAnnotation( idPropertyOnBaseClass.getAttributeMember() )
+						// determine if the @Id or @EmbeddedId tpe is the same
+						&& isIdClassOfAssociatedEntity( compositeClass, propertyAccessor, context, idPropertyType );
+				}
+				else {
+					// The associated entity has an @IdClass, so check if it's the same
+					final IdClass idClass =
+							associatedClassWithIdClass.getAnnotationUsage( IdClass.class, modelsContext() );
+					return compositeClass.getName().equals( idClass.value().getName() );
+				}
 			}
 		}
 		else {
+			// There are multiple @Id fields, so we know for sure that the id class of
+			// this entity can't be the identifier type of the associated entity
+			return false;
+		}
+	}
+
+	private static boolean isIdClassOfAssociatedEntity(
+			ClassDetails compositeClass,
+			AccessType propertyAccessor,
+			MetadataBuildingContext context,
+			TypeDetails idPropertyType) {
+		// Determine the @Id type or @EmbeddedId class of the associated entity
+		final var propertyContainer =
+				new PropertyContainer( idPropertyType.determineRawClass(), idPropertyType, propertyAccessor );
+		final List<PropertyData> idProperties = new ArrayList<>();
+		final int idPropertyCount = addElementsOfClass( idProperties, propertyContainer, context, 0 );
+		if ( idPropertyCount == 1 ) {
+			// Exactly one @Id or @EmbeddedId attribute
+			final PropertyData idPropertyOfAssociatedEntity = idProperties.get( 0 );
+			return compositeClass.getName()
+					.equals( idPropertyOfAssociatedEntity.getPropertyType().getName() );
+		}
+		else {
+			// No id property found in the associated class,
+			// or multiple id properties but no @IdClass
 			return false;
 		}
 	}

hibernate-core/src/test/java/x/IdClassSingleOneToOneTest.java

@@ -0,0 +1,104 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package x;
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.FetchType;
+import jakarta.persistence.Id;
+import jakarta.persistence.IdClass;
+import jakarta.persistence.OneToOne;
+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.Test;
+
+import java.util.Objects;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+
+@DomainModel( annotatedClasses = {
+		IdClassSingleOneToOneTest.EntityA.class,
+		IdClassSingleOneToOneTest.EntityB.class,
+} )
+@SessionFactory
+public class IdClassSingleOneToOneTest {
+
+	@Test
+	public void test(SessionFactoryScope scope) {
+		scope.getSessionFactory();
+		scope.inTransaction( session -> {
+			EntityA entityA = new EntityA(3);
+			EntityB entityB = new EntityB( entityA );
+			entityA.entityB = entityB;
+			session.persist( entityA );
+			session.persist( entityB );
+			assertEquals( new EntityBId(3),
+					session.getIdentifier( entityB ) );
+		} );
+		scope.inTransaction( session -> {
+			EntityB entityB = session.find( EntityB.class, new EntityBId(3) );
+			assertNotNull( entityB );
+		} );
+	}
+
+	@Entity( name = "EntityA" )
+	static class EntityA {
+
+		@Id
+		private Integer id;
+
+		@OneToOne( mappedBy = "entityA", fetch = FetchType.LAZY )
+		private EntityB entityB;
+
+		public EntityA() {
+		}
+
+		public EntityA(Integer id) {
+			this.id = id;
+		}
+
+	}
+
+	@IdClass( EntityBId.class )
+	@Entity( name = "EntityB" )
+	static class EntityB {
+
+		@Id
+		@OneToOne( fetch = FetchType.LAZY )
+		private EntityA entityA;
+
+		public EntityB() {
+		}
+
+		public EntityB(EntityA entityA) {
+			this.entityA = entityA;
+		}
+
+	}
+
+	static class EntityBId {
+		private final Integer entityA;
+
+		EntityBId() {
+			entityA = null;
+		}
+		EntityBId(Integer entityA) {
+			this.entityA = entityA;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+			return o instanceof EntityBId entityBId
+				&& Objects.equals( entityA, entityBId.entityA );
+		}
+
+		@Override
+		public int hashCode() {
+			return Objects.hashCode( entityA );
+		}
+	}
+}