HHH-19320 Pass current entity identifier value to generate method

Author: mbladel

Diff for: hibernate-core/src/main/java/org/hibernate/event/internal/AbstractSaveEventListener.java

@@ -152,7 +152,8 @@ private static Object generateId(
 			EventSource source,
 			BeforeExecutionGenerator generator,
 			EntityPersister persister) {
-		final Object id = generator.generate( source, entity, null, INSERT );
+		final Object currentValue = generator.allowAssignedIdentifiers() ? persister.getIdentifier( entity ) : null;
+		final Object id = generator.generate( source, entity, currentValue, INSERT );
 		if ( id == null ) {
 			throw new IdentifierGenerationException( "Null id generated for entity '" + persister.getEntityName() + "'" );
 		}

Diff for: hibernate-core/src/main/java/org/hibernate/id/CompositeNestedGeneratedValueGenerator.java

@@ -14,9 +14,12 @@
 import org.hibernate.boot.model.relational.ExportableProducer;
 import org.hibernate.boot.model.relational.SqlStringGenerationContext;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
+import org.hibernate.generator.BeforeExecutionGenerator;
 import org.hibernate.property.access.spi.Setter;
 import org.hibernate.type.CompositeType;
 
+import static org.hibernate.generator.EventType.INSERT;
+
 /**
  * For composite identifiers, defines a number of "nested" generations that
  * need to happen to "fill" the identifier property(s).
@@ -71,7 +74,6 @@ public interface GenerationContextLocator {
 	 * determined {@linkplain GenerationContextLocator#locateGenerationContext context}
 	 */
 	public interface GenerationPlan extends ExportableProducer {
-
 		/**
 		 * Initializes this instance, in particular pre-generates SQL as necessary.
 		 * <p>
@@ -82,12 +84,9 @@ public interface GenerationPlan extends ExportableProducer {
 		void initialize(SqlStringGenerationContext context);
 
 		/**
-		 * Execute the value generation.
-		 *
-		 * @param session The current session
-		 * @param incomingObject The entity for which we are generating id
+		 * Retrieve the generator for this generation plan
 		 */
-		Object execute(SharedSessionContractImplementor session, Object incomingObject);
+		BeforeExecutionGenerator getGenerator();
 
 		/**
 		 * Returns the {@link Setter injector} for the generated property.
@@ -129,7 +128,17 @@ public Object generate(SharedSessionContractImplementor session, Object object)
 				null :
 				new ArrayList<>( generationPlans.size() );
 		for ( GenerationPlan generationPlan : generationPlans ) {
-			final Object generated = generationPlan.execute( session, object );
+			final BeforeExecutionGenerator generator = generationPlan.getGenerator();
+			final Object generated;
+			if ( generator.generatedBeforeExecution( object, session ) ) {
+				final Object currentValue = generator.allowAssignedIdentifiers() ?
+						compositeType.getPropertyValue( context, generationPlan.getPropertyIndex(), session ) :
+						null;
+				generated = generator.generate( session, object, currentValue, INSERT );
+			}
+			else {
+				throw new IdentifierGenerationException( "Identity generation isn't supported for composite ids" );
+			}
 			if ( generatedValues != null ) {
 				generatedValues.add( generated );
 			}

Diff for: hibernate-core/src/main/java/org/hibernate/internal/StatelessSessionImpl.java

@@ -191,7 +191,8 @@ public Object insert(String entityName, Object entity) {
 			if ( !generator.generatesOnInsert() ) {
 				throw new IdentifierGenerationException( "Identifier generator must generate on insert" );
 			}
-			id = ( (BeforeExecutionGenerator) generator ).generate( this, entity, null, INSERT );
+			final Object currentValue = generator.allowAssignedIdentifiers() ? persister.getIdentifier( entity ) : null;
+			id = ( (BeforeExecutionGenerator) generator ).generate( this, entity, currentValue, INSERT );
 			persister.setIdentifier( entity, id, this );
 			if ( firePreInsert(entity, id, state, persister) ) {
 				return id;

Diff for: hibernate-core/src/main/java/org/hibernate/mapping/Component.java

@@ -55,7 +55,6 @@
 
 import static java.util.Collections.unmodifiableList;
 import static java.util.stream.Collectors.toList;
-import static org.hibernate.generator.EventType.INSERT;
 import static org.hibernate.internal.util.StringHelper.qualify;
 import static org.hibernate.mapping.MappingHelper.checkPropertyColumnDuplication;
 import static org.hibernate.mapping.MappingHelper.classForName;
@@ -790,13 +789,8 @@ public int getPropertyIndex() {
 		}
 
 		@Override
-		public Object execute(SharedSessionContractImplementor session, Object incomingObject) {
-			if ( generator.generatedBeforeExecution( incomingObject, session ) ) {
-				return generator.generate( session, incomingObject, null, INSERT );
-			}
-			else {
-				throw new IdentifierGenerationException( "Identity generation isn't supported for composite ids" );
-			}
+		public BeforeExecutionGenerator getGenerator() {
+			return generator;
 		}
 
 		@Override