Introduce `VirtualIdEmbeddable` and `IdClassEmbeddable` + instantiators

Prep work for EmbeddableInstantiator - initializer

Still need to
  - integrate EmbeddableInstantiator work
  - integrate embedded forms.  `VirtualIdEmbeddable` does not really need it as it can use the id-mapping itself as the embedded form.  But `IdClassEmbedded` should really be integrated
  - integrate `VirtualKeyEmbeddable` and `VirtualKeyEmbedded` for use as inverse composite fks
  - share `#finishInit` handling for `EmbeddableMappingType`, `VirtualIdEmbeddable` and `IdClassEmbeddable`
  - ability to use the containing composite owner as the parent of a composite (legacy behavior is to always use the "first" entity

hibernate-core/src/main/java/org/hibernate/engine/spi/EntityKey.java

@@ -48,7 +48,7 @@ public final class EntityKey implements Serializable {
 	public EntityKey(Object id, EntityPersister persister) {
 		this.persister = persister;
 		if ( id == null ) {
-			throw new AssertionFailure( "null identifier" );
+			throw new AssertionFailure( "null identifier (" + persister.getEntityName() + ")" );
 		}
 		this.identifier = id;
 		this.hashCode = generateHashCode();

hibernate-core/src/main/java/org/hibernate/metamodel/mapping/AttributeMapping.java

@@ -6,6 +6,7 @@
  */
 package org.hibernate.metamodel.mapping;
 
+import org.hibernate.engine.spi.SessionFactoryImplementor;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.property.access.spi.PropertyAccess;
 import org.hibernate.sql.results.graph.Fetchable;
@@ -39,11 +40,22 @@ public interface AttributeMapping extends ModelPart, ValueMapping, Fetchable, Pr
 	 * Convenient access to getting the value for this attribute from the "owner"
 	 */
 	default Object getValue(Object container, SharedSessionContractImplementor session) {
+		return getValue( container, session.getSessionFactory() );
+	}
+
+	/**
+	 * Convenient access to getting the value for this attribute from the "owner"
+	 */
+	default Object getValue(Object container, SessionFactoryImplementor sessionFactory) {
 		return getPropertyAccess().getGetter().get( container );
 	}
 
 	default void setValue(Object container, Object value, SharedSessionContractImplementor session) {
-		getPropertyAccess().getSetter().set( container, value, session.getSessionFactory() );
+		setValue( container, value, session.getSessionFactory() );
+	}
+
+	default void setValue(Object container, Object value, SessionFactoryImplementor sessionFactory) {
+		getPropertyAccess().getSetter().set( container, value, sessionFactory );
 	}
 
 	/**

hibernate-core/src/main/java/org/hibernate/metamodel/mapping/internal/EmbeddableMappingTypeImpl.java

@@ -811,12 +811,8 @@ public class EmbeddableMappingTypeImpl implements EmbeddableMappingType, Selecta
 		}
 
 		for ( int i = 0; i < attributeMappings.size(); i++ ) {
-			attributeMappings.get( i )
-					.getAttributeMetadataAccess()
-					.resolveAttributeMetadata( null )
-					.getPropertyAccess()
-					.getSetter()
-					.set( compositeInstance, resolvedValues[i], sessionFactory );
+			final AttributeMapping attributeMapping = attributeMappings.get( i );
+			attributeMapping.setValue( compositeInstance, resolvedValues[i], sessionFactory );
 		}
 	}
 

hibernate-core/src/main/java/org/hibernate/sql/results/graph/embeddable/AbstractEmbeddableInitializer.java

@@ -29,12 +29,14 @@ import org.hibernate.sql.results.graph.Fetch;
 import org.hibernate.sql.results.graph.FetchParentAccess;
 import org.hibernate.sql.results.graph.Initializer;
 import org.hibernate.sql.results.graph.collection.CollectionInitializer;
-import org.hibernate.sql.results.graph.entity.AbstractEntityInitializer;
 import org.hibernate.sql.results.graph.entity.EntityInitializer;
 import org.hibernate.sql.results.internal.NullValueAssembler;
 import org.hibernate.sql.results.jdbc.spi.RowProcessingState;
+import org.hibernate.type.descriptor.java.JavaType;
 import org.hibernate.type.descriptor.java.spi.EntityJavaTypeDescriptor;
 
+import static java.lang.Boolean.FALSE;
+import static java.lang.Boolean.TRUE;
 import static org.hibernate.internal.util.collections.CollectionHelper.arrayList;
 
 /**
@@ -85,6 +87,10 @@ public abstract class AbstractEmbeddableInitializer extends AbstractFetchParentA
 		this.resolvedValues = new Object[ numOfAttrs ];
 		this.assemblers = arrayList( numOfAttrs );
 
+		// todo (6.0) - why not just use the "maps id" form right here?
+		//		( (CompositeIdentifierMapping) embedded ).getMappedIdEmbeddableTypeDescriptor()
+		//		in theory this should let us avoid the explicit maps-id handling via `setPropertyValuesOnTarget`
+
 		embeddableTypeDescriptor.visitFetchables(
 				stateArrayContributor -> {
 					final Fetch fetch = resultDescriptor.findFetch( stateArrayContributor );
@@ -126,12 +132,21 @@ public abstract class AbstractEmbeddableInitializer extends AbstractFetchParentA
 	}
 
 	@Override
-	public void resolveKey(RowProcessingState rowProcessingState) {
+	public FetchParentAccess findFirstEntityDescriptorAccess() {
+		return getFetchParentAccess().findFirstEntityDescriptorAccess();
+	}
+
+	@Override
+	public void resolveKey(RowProcessingState processingState) {
 		// nothing to do
 	}
 
 	@Override
-	public void resolveInstance(RowProcessingState rowProcessingState) {
+	public void resolveInstance(RowProcessingState processingState) {
+		reallyResolve( processingState );
+	}
+
+	private void reallyResolve(RowProcessingState processingState) {
 		if ( compositeInstance != null ) {
 			return;
 		}
@@ -140,14 +155,25 @@ public abstract class AbstractEmbeddableInitializer extends AbstractFetchParentA
 		// which we access through the fetch parent access.
 		// If this model part is an identifier, we must construct the instance as this is called during resolveKey
 		final EmbeddableMappingType embeddableTypeDescriptor = embedded.getEmbeddableTypeDescriptor();
+		final JavaType<?> embeddableJtd = embeddableTypeDescriptor.getMappedJavaTypeDescriptor();
 
-		if ( fetchParentAccess != null && embeddableTypeDescriptor.getMappedJavaTypeDescriptor().getJavaTypeClass()
-				.isAssignableFrom( fetchParentAccess.getInitializedPart().getJavaTypeDescriptor().getJavaTypeClass() )
-				&& embeddableTypeDescriptor.getMappedJavaTypeDescriptor() instanceof EntityJavaTypeDescriptor<?>
+		if ( fetchParentAccess != null &&
+				embeddableJtd.getJavaTypeClass().isAssignableFrom( fetchParentAccess.getInitializedPart().getJavaTypeDescriptor().getJavaTypeClass() )
+				&& embeddableJtd instanceof EntityJavaTypeDescriptor<?>
 				&& !( embedded instanceof CompositeIdentifierMapping )
 				&& !EntityIdentifierMapping.ROLE_LOCAL_NAME.equals( embedded.getFetchableName() ) ) {
-			fetchParentAccess.resolveInstance( rowProcessingState );
+			EmbeddableLoadingLogger.INSTANCE.debugf(
+					"Linking composite instance to fetch-parent [%s] - %s",
+					navigablePath,
+					fetchParentAccess
+			);
+			fetchParentAccess.resolveInstance( processingState );
 			compositeInstance = fetchParentAccess.getInitializedInstance();
+			EmbeddableLoadingLogger.INSTANCE.debugf(
+					"Done linking composite instance to fetch-parent [%s] - %s",
+					navigablePath,
+					compositeInstance
+			);
 		}
 
 		if ( compositeInstance == null ) {
@@ -164,37 +190,24 @@ public abstract class AbstractEmbeddableInitializer extends AbstractFetchParentA
 
 	@Override
 	public void initializeInstance(RowProcessingState processingState) {
-		final Initializer initializer = processingState.resolveInitializer( navigablePath.getParent() );
-
-		handleParentInjection( processingState );
-
 		EmbeddableLoadingLogger.INSTANCE.debugf(
 				"Initializing composite instance [%s]",
 				navigablePath
 		);
 
-		boolean areAllValuesNull = true;
-		for ( int i = 0; i < assemblers.size(); i++ ) {
-			final DomainResultAssembler<?> assembler = assemblers.get( i );
-			final Object contributorValue = assembler.assemble(
-					processingState,
-					processingState.getJdbcValuesSourceProcessingState().getProcessingOptions()
-			);
+		handleParentInjection( processingState );
 
-			resolvedValues[i] = contributorValue;
-			if ( contributorValue != null ) {
-				areAllValuesNull = false;
-			}
-		}
+		extractRowState( processingState );
 
-		if ( !createEmptyCompositesEnabled && areAllValuesNull ) {
+		if ( !createEmptyCompositesEnabled && allValuesNull == TRUE ) {
 			compositeInstance = null;
 		}
 		else {
 			notifyResolutionListeners( compositeInstance );
 			if ( compositeInstance instanceof HibernateProxy ) {
-				if ( initializer != this ) {
-					( (AbstractEntityInitializer) initializer ).registerResolutionListener(
+				final Initializer parentInitializer = processingState.resolveInitializer( navigablePath.getParent() );
+				if ( parentInitializer != this ) {
+					( (FetchParentAccess) parentInitializer ).registerResolutionListener(
 							entity -> setPropertyValuesOnTarget( entity, processingState.getSession() )
 					);
 				}
@@ -214,11 +227,28 @@ public abstract class AbstractEmbeddableInitializer extends AbstractFetchParentA
 			// A possible alternative could be to initialize the resolved values for primitive fields to their default value,
 			// but that might cause unexpected outcomes for Hibernate 5 users that use createEmptyCompositesEnabled when updating.
 			// You can see the need for this by running EmptyCompositeEquivalentToNullTest
-			else if ( !areAllValuesNull ) {
+			else if ( allValuesNull == FALSE ) {
 				setPropertyValuesOnTarget( compositeInstance, processingState.getSession() );
 			}
 		}
 	}
+
+	private void extractRowState(RowProcessingState processingState) {
+		allValuesNull = true;
+		for ( int i = 0; i < assemblers.size(); i++ ) {
+			final DomainResultAssembler<?> assembler = assemblers.get( i );
+			final Object contributorValue = assembler.assemble(
+					processingState,
+					processingState.getJdbcValuesSourceProcessingState().getProcessingOptions()
+			);
+
+			resolvedValues[i] = contributorValue;
+			if ( contributorValue != null ) {
+				allValuesNull = false;
+			}
+		}
+	}
+
 	private void handleParentInjection(RowProcessingState processingState) {
 		final PropertyAccess parentInjectionAccess = embedded.getParentInjectionAttributePropertyAccess();
 		if ( parentInjectionAccess == null ) {
@@ -229,8 +259,7 @@ public abstract class AbstractEmbeddableInitializer extends AbstractFetchParentA
 		// todo (6.0) : should we initialize the composite instance if we get here and it is null (not NULL_MARKER)?
 
 		// we want to avoid injection for `NULL_MARKER`
-		final Object compositeInstance = getCompositeInstance();
-		if ( compositeInstance == null ) {
+		if ( compositeInstance == null || compositeInstance == NULL_MARKER ) {
 			EmbeddableLoadingLogger.INSTANCE.debugf(
 					"Skipping parent injection for null embeddable [%s]",
 					navigablePath
@@ -342,11 +371,12 @@ public abstract class AbstractEmbeddableInitializer extends AbstractFetchParentA
 	@Override
 	public void finishUpRow(RowProcessingState rowProcessingState) {
 		compositeInstance = null;
+		allValuesNull = null;
 		clearResolutionListeners();
 	}
 
 	@Override
-	public FetchParentAccess findFirstEntityDescriptorAccess() {
-		return getFetchParentAccess().findFirstEntityDescriptorAccess();
+	public String toString() {
+		return getClass().getSimpleName() + "(" + navigablePath + ") : `" + getInitializedPart().getJavaTypeDescriptor().getJavaTypeClass() + "`";
 	}
 }

hibernate-core/src/test/java/org/hibernate/orm/test/mapping/cid/idclass/Customer.java

@@ -0,0 +1,44 @@
+/*
+ * 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.orm.test.mapping.cid.idclass; /**
+ * @author Steve Ebersole
+ */
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.Table;
+import jakarta.persistence.Id;
+import jakarta.persistence.Basic;
+
+@Entity(name = "Customer")
+@Table(name = "customers")
+public class Customer {
+	@Id
+	public Integer id;
+	@Basic
+	public String name;
+
+	protected Customer() {
+		// for Hibernate use
+	}
+
+	public Customer(Integer id, String name) {
+		this.id = id;
+		this.name = name;
+	}
+
+	public Integer getId() {
+		return id;
+	}
+
+	public String getName() {
+		return name;
+	}
+
+	public void setName(String name) {
+		this.name = name;
+	}
+}

hibernate-core/src/test/java/org/hibernate/orm/test/mapping/cid/idclass/NestedIdClassTests.java

@@ -0,0 +1,103 @@
+/*
+ * 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.orm.test.mapping.cid.idclass;
+
+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.AfterEach;
+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 = {
+		Customer.class,
+		Order.class,
+		Payment.class
+})
+@SessionFactory
+public class NestedIdClassTests {
+	@Test
+	public void smokeTest(SessionFactoryScope scope) {
+		scope.inTransaction( (session) -> {
+			final String qry = "from Payment p join fetch p.id.order o join fetch o.id.customer";
+			session.createQuery( qry ).list();
+		});
+		scope.inTransaction( (session) -> {
+			final String qry = "from Payment p join fetch p.order o join fetch o.customer";
+			session.createQuery( qry ).list();
+		});
+	}
+
+	@Test
+	public void smokeTest2(SessionFactoryScope scope) {
+		scope.inTransaction( (session) -> {
+			final String qry = "from Payment p";
+			final Payment payment = session.createQuery( qry, Payment.class ).uniqueResult();
+			assertThat( payment ).isNotNull();
+			assertThat( payment.accountNumber ).isNotNull();
+			assertThat( payment.order ).isNotNull();
+
+			assertThat( payment.order.orderNumber ).isNotNull();
+			assertThat( payment.order.customer ).isNotNull();
+
+			assertThat( payment.order.customer.id ).isNotNull();
+			assertThat( payment.order.customer.name ).isNotNull();
+		});
+		scope.inTransaction( (session) -> {
+			final String qry = "from Payment p join fetch p.order o join fetch o.customer";
+			session.createQuery( qry ).list();
+		});
+	}
+
+	@Test
+	public void smokeTest3(SessionFactoryScope scope) {
+		scope.inTransaction( (session) -> {
+			final Payment payment = session.get( Payment.class, new PaymentId( new OrderId( 1, 1 ), "123" ) );
+			assertThat( payment ).isNotNull();
+			assertThat( payment.accountNumber ).isNotNull();
+			assertThat( payment.order ).isNotNull();
+
+			assertThat( payment.order.orderNumber ).isNotNull();
+			assertThat( payment.order.customer ).isNotNull();
+
+			assertThat( payment.order.customer.id ).isNotNull();
+			assertThat( payment.order.customer.name ).isNotNull();
+		});
+	}
+
+	@BeforeEach
+	public void createTestData(SessionFactoryScope scope) {
+		scope.inTransaction( (session) -> {
+			final Customer acme = new Customer( 1, "acme" );
+			final Customer spacely = new Customer( 2, "spacely" );
+			session.persist( acme );
+			session.persist( spacely );
+
+			final Order acmeOrder1 = new Order( acme, 1, 123F );
+			final Order acmeOrder2 = new Order( acme, 2, 123F );
+			session.persist( acmeOrder1 );
+			session.persist( acmeOrder2 );
+
+			final Payment payment = new Payment( acmeOrder1, "123" );
+			session.persist( payment );
+		} );
+	}
+
+	@AfterEach
+	public void dropTestData(SessionFactoryScope scope) {
+		scope.inTransaction( (session) -> {
+			session.createQuery( "delete Payment" ).executeUpdate();
+			session.createQuery( "delete Order" ).executeUpdate();
+			session.createQuery( "delete Customer" ).executeUpdate();
+		} );
+	}
+}

hibernate-core/src/test/java/org/hibernate/orm/test/mapping/cid/idclass/Order.java

@@ -0,0 +1,63 @@
+/*
+ * 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.orm.test.mapping.cid.idclass; /**
+ * @author Steve Ebersole
+ */
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.IdClass;
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.Table;
+
+@Entity(name = "Order")
+@Table(name = "orders")
+@IdClass( OrderId.class )
+public class Order {
+	@Id
+	@ManyToOne
+	public Customer customer;
+
+	@Id
+	public Integer orderNumber;
+
+	public Float amount;
+
+	protected Order() {
+		// for Hibernate use
+	}
+
+	public Order(Customer customer, Integer orderNumber, Float amount) {
+		this.customer = customer;
+		this.orderNumber = orderNumber;
+		this.amount = amount;
+	}
+
+	public Customer getCustomer() {
+		return customer;
+	}
+
+	public void setCustomer(Customer customer) {
+		this.customer = customer;
+	}
+
+	public Integer getOrderNumber() {
+		return orderNumber;
+	}
+
+	public void setOrderNumber(Integer orderNumber) {
+		this.orderNumber = orderNumber;
+	}
+
+	public Float getAmount() {
+		return amount;
+	}
+
+	public void setAmount(Float amount) {
+		this.amount = amount;
+	}
+}

hibernate-core/src/test/java/org/hibernate/orm/test/mapping/cid/idclass/OrderId.java

@@ -0,0 +1,23 @@
+/*
+ * 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.orm.test.mapping.cid.idclass;
+
+/**
+ * @author Steve Ebersole
+ */
+public class OrderId {
+	Integer customer;
+	Integer orderNumber;
+
+	public OrderId() {
+	}
+
+	public OrderId(Integer customer, Integer orderNumber) {
+		this.customer = customer;
+		this.orderNumber = orderNumber;
+	}
+}

hibernate-core/src/test/java/org/hibernate/orm/test/mapping/cid/idclass/Payment.java

@@ -0,0 +1,53 @@
+/*
+ * 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.orm.test.mapping.cid.idclass; /**
+ * @author Steve Ebersole
+ */
+
+import jakarta.persistence.Basic;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.IdClass;
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.Table;
+
+@Entity(name = "Payment")
+@Table(name = "payments")
+@IdClass( PaymentId.class )
+public class Payment {
+	@Id
+	@ManyToOne
+	public Order order;
+
+	@Basic
+	public String accountNumber;
+
+	protected Payment() {
+		// for Hibernate use
+	}
+
+	public Payment(Order order, String accountNumber) {
+		this.order = order;
+		this.accountNumber = accountNumber;
+	}
+
+	public Order getOrder() {
+		return order;
+	}
+
+	public void setOrder(Order order) {
+		this.order = order;
+	}
+
+	public String getAccountNumber() {
+		return accountNumber;
+	}
+
+	public void setAccountNumber(String accountNumber) {
+		this.accountNumber = accountNumber;
+	}
+}

hibernate-core/src/test/java/org/hibernate/orm/test/mapping/cid/idclass/PaymentId.java

@@ -0,0 +1,23 @@
+/*
+ * 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.orm.test.mapping.cid.idclass;
+
+/**
+ * @author Steve Ebersole
+ */
+public class PaymentId {
+	private OrderId order;
+	private String accountNumber;
+
+	public PaymentId() {
+	}
+
+	public PaymentId(OrderId order, String accountNumber) {
+		this.order = order;
+		this.accountNumber = accountNumber;
+	}
+}