HHH-8276 - Integrate LoadPlans into UniqueEntityLoader (PoC)

Author: gbadner

hibernate-core/src/main/java/org/hibernate/loader/plan2/build/internal/returns/AbstractCollectionReference.java

@@ -95,11 +95,11 @@ private CollectionFetchableElement buildElementGraph(
 		final Type type = persister.getElementType();
 		if ( type.isAssociationType() ) {
 			if ( type.isEntityType() ) {
-				final EntityPersister indexPersister = persister.getFactory().getEntityPersister(
+				final EntityPersister elementPersister = persister.getFactory().getEntityPersister(
 						( (EntityType) type ).getAssociatedEntityName()
 				);
 
-				final Join join = collectionQuerySpace.addElementEntityJoin( indexPersister, loadPlanBuildingContext );
+				final Join join = collectionQuerySpace.addElementEntityJoin( elementPersister, loadPlanBuildingContext );
 				return new CollectionFetchableElementEntityGraph( this, join );
 			}
 		}

hibernate-core/src/main/java/org/hibernate/loader/plan2/build/internal/returns/EntityFetchImpl.java

@@ -89,12 +89,6 @@ public String[] toSqlSelectFragments(String alias) {
 
 	@Override
 	public void validateFetchPlan(FetchStrategy fetchStrategy, AttributeDefinition attributeDefinition) {
-		if ( attributeDefinition.getType().isCollectionType() ) {
-			throw new WalkingException(
-					"Encountered collection attribute in identifier fetches: " + attributeDefinition.getSource() +
-							"." + attributeDefinition.getName()
-			);
-		}
 		// todo : allow bi-directional key-many-to-one fetches?
 		//		those do cause problems in Loader; question is whether those are indicative of that situation or
 		// 		of Loaders ability to handle it.

hibernate-core/src/main/java/org/hibernate/loader/plan2/build/internal/spaces/CollectionQuerySpaceImpl.java

@@ -29,6 +29,7 @@
 import org.hibernate.loader.plan2.spi.CollectionQuerySpace;
 import org.hibernate.loader.plan2.spi.Join;
 import org.hibernate.persister.collection.CollectionPersister;
+import org.hibernate.persister.collection.QueryableCollection;
 import org.hibernate.persister.entity.EntityPersister;
 import org.hibernate.persister.entity.PropertyMapping;
 import org.hibernate.persister.entity.Queryable;

hibernate-core/src/main/java/org/hibernate/loader/plan2/exec/internal/LoadQueryJoinAndFetchProcessor.java

@@ -125,7 +125,12 @@ private void renderJoin(Join join, JoinFragment joinFragment) {
 			handleCompositeJoin( join, joinFragment );
 		}
 		else if ( EntityQuerySpace.class.isInstance( join.getRightHandSide() ) ) {
-			renderEntityJoin( join, joinFragment );
+			// do not render the entity join for a one-to-many association, since the collection join
+			// already joins to the associated entity table (see doc in renderCollectionJoin()).
+			if ( join.getLeftHandSide().getDisposition() != QuerySpace.Disposition.COLLECTION ||
+					! CollectionQuerySpace.class.cast( join.getLeftHandSide() ).getCollectionPersister().isOneToMany() ) {
+				renderEntityJoin( join, joinFragment );
+			}
 		}
 		else if ( CollectionQuerySpace.class.isInstance( join.getRightHandSide() ) ) {
 			renderCollectionJoin( join, joinFragment );
@@ -249,14 +254,14 @@ private void renderCollectionJoin(Join join, JoinFragment joinFragment) {
 				rightHandSide.getCollectionPersister()
 		);
 
-		// if the collection being joined is a one-to-many there is actually nothing to render here - there will
-		// be a follow-on join (rhs will have a join) for the associated entity.
+		// The SQL join to the "collection table" needs to be rendered.
 		//
-		// otherwise the SQL join to the "collection table" needs to be rendered.  In the case of a basic collection,
-		// that's the only join needed.  For many-to-many, we need to render the "collection table join" here (as
-		// already stated), but joining to the entity element table is handled by a follow-on join for the associated
-		// entity as discussed with regard to one-to-many
+		// In the case of a basic collection, that's the only join needed.
 		//
+		// For one-to-many/many-to-many, we need to render the "collection table join"
+		// here (as already stated). There will be a follow-on join (rhs will have a join) for the associated entity.
+		// For many-to-many, the follow-on join will join to the associated entity element table. For one-to-many,
+		// the collection table is the associated entity table, so the follow-on join will not be rendered..
 
 		if ( rightHandSide.getCollectionPersister().isOneToMany()
 				|| rightHandSide.getCollectionPersister().isManyToMany() ) {
@@ -298,11 +303,6 @@ private void renderCollectionJoin(Join join, JoinFragment joinFragment) {
 			);
 		}
 
-		if ( rightHandSide.getCollectionPersister().isOneToMany() ) {
-			// as stated, nothing to do...
-			return;
-		}
-
 		renderSqlJoinToCollectionTable(
 				aliases,
 				rightHandSide,