HHH-18829 Main:

- Hibernate Processor - create ID class in meta data class if entity class with more than
          one ID component is not annotated with @IdClass; property order must be preserved
    - Hibernate Core - if entity class has more than one ID component, but is not annotated with @IdClass
          entity binder should try to use ID class from metamodel if generated

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

@@ -481,10 +481,22 @@ public class EntityBinder {
 		final ClassDetails classWithIdClass = inheritanceState.getClassWithIdClass( false );
 		if ( classWithIdClass != null ) {
 			final IdClass idClassAnn = classWithIdClass.getDirectAnnotationUsage( IdClass.class );
-			final Class<?> idClassValue = idClassAnn.value();
-			final ClassDetails compositeClass =
-					getMetadataCollector().getSourceModelBuildingContext().getClassDetailsRegistry()
-							.resolveClassDetails( idClassValue.getName() );
+			final ClassDetails compositeClass;
+			if ( idClassAnn == null ) {
+				try {
+					compositeClass = getMetadataCollector().getSourceModelBuildingContext()
+							.getClassDetailsRegistry()
+							.resolveClassDetails( inheritanceState.getClassDetails().getClassName() + "_$Id" );
+				}
+				catch (RuntimeException e) {
+					return false;
+				}
+			}
+			else {
+				final Class<?> idClassValue = idClassAnn.value();
+				compositeClass = getMetadataCollector().getSourceModelBuildingContext()
+						.getClassDetailsRegistry().resolveClassDetails( idClassValue.getName() );
+			}
 			final TypeDetails compositeType = new ClassTypeDetailsImpl( compositeClass, TypeDetails.Kind.CLASS );
 			final TypeDetails classWithIdType = new ClassTypeDetailsImpl( classWithIdClass, TypeDetails.Kind.CLASS );
 

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

@@ -7,6 +7,7 @@ package org.hibernate.boot.model.internal;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
+import java.util.stream.Stream;
 
 import org.hibernate.AnnotationException;
 import org.hibernate.boot.spi.AccessType;
@@ -183,6 +184,13 @@ public class InheritanceState {
 			return classDetails;
 		}
 		else {
+			final long count = Stream.concat(
+					classDetails.getFields().stream(),
+					classDetails.getMethods().stream()
+			).filter( t -> t.hasDirectAnnotationUsage( Id.class ) ).count();
+			if ( count > 1 ) {
+				return classDetails;
+			}
 			final InheritanceState state = getSuperclassInheritanceState( classDetails, inheritanceStatePerClass );
 			if ( state != null ) {
 				return state.getClassWithIdClass( true );

tooling/metamodel-generator/src/main/java/org/hibernate/processor/annotation/AnnotationMetaEntity.java

@@ -108,6 +108,8 @@ import static org.hibernate.processor.util.TypeUtils.propertyName;
  */
 public class AnnotationMetaEntity extends AnnotationMeta {
 
+	private static final String ID_CLASS_MEMBER_NAME = "<ID_CLASS>";
+
 	private final ImportContext importContext;
 	private final TypeElement element;
 	private final Map<String, MetaAttribute> members;
@@ -438,6 +440,8 @@ public class AnnotationMetaEntity extends AnnotationMeta {
 
 			addPersistentMembers( fieldsOfClass, AccessType.FIELD );
 			addPersistentMembers( gettersAndSettersOfClass, AccessType.PROPERTY );
+
+			addIdClassIfNeeded( fieldsOfClass, gettersAndSettersOfClass );
 		}
 
 		addAuxiliaryMembers();
@@ -451,6 +455,33 @@ public class AnnotationMetaEntity extends AnnotationMeta {
 		initialized = true;
 	}
 
+	private void addIdClassIfNeeded(List<? extends Element> fields, List<? extends Element> methods) {
+		if ( hasAnnotation( element, ID_CLASS ) ) {
+			return;
+		}
+		final List<MetaAttribute> components = new ArrayList<>();
+		for ( Element field : fields ) {
+			if ( hasAnnotation( field, ID ) && isPersistent( field, AccessType.FIELD ) ) {
+				final String propertyName = propertyName( this, field );
+				if ( members.containsKey( propertyName ) ) {
+					components.add( members.get( propertyName ) );
+				}
+			}
+		}
+		for ( Element method : methods ) {
+			if ( hasAnnotation( method, ID ) && isPersistent( method, AccessType.PROPERTY ) ) {
+				final String propertyName = propertyName( this, method );
+				if ( members.containsKey( propertyName ) ) {
+					components.add( members.get( propertyName ) );
+				}
+			}
+		}
+		if ( components.size() < 2 ) {
+			return;
+		}
+		putMember( ID_CLASS_MEMBER_NAME, new IdClassMetaAttribute( this, components ) );
+	}
+
 	private boolean checkEntities(List<ExecutableElement> lifecycleMethods) {
 		boolean foundPersistenceEntity = false;
 		VariableElement nonPersistenceParameter = null;

tooling/metamodel-generator/src/main/java/org/hibernate/processor/annotation/AnnotationMetaSingleAttribute.java

@@ -4,11 +4,15 @@
  */
 package org.hibernate.processor.annotation;
 
+import javax.lang.model.element.AnnotationMirror;
 import javax.lang.model.element.Element;
 
 import org.hibernate.processor.model.MetaSingleAttribute;
 import org.hibernate.processor.util.Constants;
 
+import java.util.ArrayList;
+import java.util.List;
+
 /**
  * @author Max Andersen
  * @author Hardy Ferentschik
@@ -24,4 +28,9 @@ public class AnnotationMetaSingleAttribute extends AnnotationMetaAttribute imple
 	public final String getMetaType() {
 		return Constants.SINGULAR_ATTRIBUTE;
 	}
+
+	@Override
+	public List<AnnotationMirror> inheritedAnnotations() {
+		return new ArrayList<>(element.getAnnotationMirrors());
+	}
 }

tooling/metamodel-generator/src/main/java/org/hibernate/processor/annotation/IdClassMetaAttribute.java

@@ -0,0 +1,73 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.processor.annotation;
+
+import org.hibernate.processor.model.MetaAttribute;
+import org.hibernate.processor.model.Metamodel;
+
+import java.util.List;
+
+public class IdClassMetaAttribute implements MetaAttribute {
+
+	private final Metamodel parent;
+
+	private final List<MetaAttribute> components;
+
+	public IdClassMetaAttribute(Metamodel parent, List<MetaAttribute> components) {
+		this.parent = parent;
+		this.components = components;
+	}
+
+	@Override
+	public boolean hasTypedAttribute() {
+		return true;
+	}
+
+	@Override
+	public boolean hasStringAttribute() {
+		return false;
+	}
+
+	@Override
+	public String getAttributeDeclarationString() {
+		final StringBuilder decl = new StringBuilder()
+				.append("\n/**\n * Static ID class for {@link ")
+				.append( parent.getQualifiedName() )
+				.append( "}\n **/\n" )
+				.append( "public record Id" );
+		String delimiter = "(";
+		for ( MetaAttribute component : components ) {
+			decl.append( delimiter ).append( parent.importType( component.getTypeDeclaration() ) )
+					.append( ' ' ).append( component.getPropertyName() );
+			delimiter = ", ";
+		}
+		return decl.append( ") {}" ).toString();
+	}
+
+	@Override
+	public String getAttributeNameDeclarationString() {
+		return "";
+	}
+
+	@Override
+	public String getMetaType() {
+		return "";
+	}
+
+	@Override
+	public String getPropertyName() {
+		return "";
+	}
+
+	@Override
+	public String getTypeDeclaration() {
+		return "";
+	}
+
+	@Override
+	public Metamodel getHostingEntity() {
+		return parent;
+	}
+}