# AggregateOneToOneAppender.java

    package org.codefilarete.stalactite.engine.configurer.resolver.onetoone;

    import org.codefilarete.reflection.AccessorChain;
    import org.codefilarete.reflection.PropertyAccessor;
    import org.codefilarete.stalactite.engine.configurer.model.ResolvedOneToOneRelation;
    import org.codefilarete.stalactite.engine.configurer.resolver.AggregateResolver.AssemblyPoint;
    import org.codefilarete.stalactite.engine.configurer.resolver.SkeletonAggregateResolver;
    import org.codefilarete.stalactite.engine.runtime.ConfiguredRelationalPersister;
    import org.codefilarete.stalactite.engine.runtime.load.EntityJoinTree;
    import org.codefilarete.stalactite.sql.ddl.structure.Table;
    import org.codefilarete.tool.function.Hanger.Holder;

    public class AggregateOneToOneAppender {

    	private final OneToOneResolver oneToOneResolver;

    	public AggregateOneToOneAppender(SkeletonAggregateResolver skeletonAggregateResolver) {
    		this.oneToOneResolver = new OneToOneResolver(skeletonAggregateResolver);
    	}

    	public <SRC, SRCID, TRGT, TRGTID, LEFTTABLE extends Table<LEFTTABLE>, RIGHTTABLE extends Table<RIGHTTABLE>, JOINID>
    	AssemblyPoint append(ConfiguredRelationalPersister<SRC, SRCID> rootPersister,
    						 ResolvedOneToOneRelation<SRC, TRGT, LEFTTABLE, RIGHTTABLE, JOINID> relationPawn,
    	                     AssemblyPoint<SRC, SRCID, TRGT, LEFTTABLE> assemblyPawn) {

    		ResolvedOneToOneRelation<SRC, TRGT, LEFTTABLE, RIGHTTABLE, JOINID> relation = relationPawn;
    		Holder<AssemblyPoint> resultHolder = new Holder<>();
    		oneToOneResolver.resolve(
    				relation,
    				assemblyPawn.getRelationOwnerPersister(),
    				targetPersister -> {
    					PropertyAccessor<SRC, TRGT> accessor;
    					if (assemblyPawn.getParentJoinPoint().equals(EntityJoinTree.ROOT_JOIN_NAME)) {
    						// this is the very first step (see stack seed) which is the root entity, no relation accessor shifting here
    						accessor = relation.getAccessor();
    					} else {
    						// we need to shift the relation accessor by the parent accessor
    						AccessorChain<SRC, TRGT> shifter = new AccessorChain<>(assemblyPawn.getAccessor(), relation.getAccessor());
    						shifter.setNullValueHandler(AccessorChain.RETURN_NULL);
    						accessor = shifter;
    					}

    					// we join the relation onto the aggregate root to build the whole select tree
    					String joinName = targetPersister.joinAsOne(
    							assemblyPawn.getParentJoinPoint(),
    							rootPersister,
    							accessor,
    							relation.getJoin().getLeftKey(),
    							relation.getJoin().getRightKey(),
    							null,
    							relation.getRelationFixer(),
    							true,
    							false);

    					resultHolder.set(new AssemblyPoint(relation.getTargetEntity(), targetPersister, joinName, accessor));
    				});
    		return resultHolder.get();
    	}
    }