HHH-18829 Hibernate Processor - ID class generation where needed

Author: cigaly

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

@@ -6,6 +6,7 @@
 
 import org.hibernate.processor.model.MetaAttribute;
 import org.hibernate.processor.model.Metamodel;
+import org.hibernate.processor.util.Constants;
 
 import javax.annotation.processing.FilerException;
 import javax.lang.model.element.ElementKind;
@@ -20,6 +21,9 @@
 import java.time.format.DateTimeFormatter;
 import java.util.List;
 
+import static org.hibernate.processor.util.TypeUtils.hasAnnotation;
+import static org.hibernate.processor.util.TypeUtils.isAnnotationMirrorOfType;
+
 /**
  * Helper class to write the actual metamodel class using the  {@link javax.annotation.processing.Filer} API.
  *
@@ -100,6 +104,8 @@ private static StringBuffer generateBody(Metamodel entity, Context context) {
 
 			pw.println();
 
+			generateIdClassIfNeeded( entity, pw );
+
 			final List<MetaAttribute> members = entity.getMembers();
 			for ( MetaAttribute metaMember : members ) {
 				if ( metaMember.hasStringAttribute() ) {
@@ -229,4 +235,24 @@ private static String writeStaticMetaModelAnnotation(Metamodel entity) {
 				: "jakarta.persistence.metamodel.StaticMetamodel";
 		return "@" + entity.importType( annotation ) + "(" + entity.getSimpleName() + ".class)";
 	}
+
+	private static void generateIdClassIfNeeded(Metamodel entity, PrintWriter pw) {
+		if ( hasAnnotation( entity.getElement(), Constants.ID_CLASS ) ) {
+			return;
+		}
+
+		final List<String> idFields = entity.getMembers().stream()
+				.filter( a -> a.inheritedAnnotations().stream()
+						.anyMatch( m -> isAnnotationMirrorOfType( m, Constants.ID ) )
+				)
+				.map( a -> entity.importType( a.getTypeDeclaration() ) + " " + a.getPropertyName() )
+				.toList();
+
+		if ( idFields.size() > 1 ) {
+			pw.print( "public record Id(" );
+			pw.print( String.join( ", ", idFields ) );
+			pw.println( ") {}" );
+			pw.println();
+		}
+	}
 }

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 AnnotationMetaSingleAttribute(AnnotationMetaEntity parent, Element elemen
 	public final String getMetaType() {
 		return Constants.SINGULAR_ATTRIBUTE;
 	}
+
+	@Override
+	public List<AnnotationMirror> inheritedAnnotations() {
+		return new ArrayList<>(element.getAnnotationMirrors());
+	}
 }