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  package org.apache.cayenne.query;
  
  import java.util.Iterator;
  
  import org.apache.cayenne.CayenneRuntimeException;
  import org.apache.cayenne.exp.Expression;
  import org.apache.cayenne.exp.ExpressionFactory;
  import org.apache.cayenne.exp.path.CayennePath;
  import org.apache.cayenne.map.EntityResolver;
  import org.apache.cayenne.map.ObjRelationship;
  import org.apache.cayenne.reflect.ClassDescriptor;
  import org.apache.cayenne.util.CayenneMapEntry;
  
  /**
   * Preprocessor and router of SelectQuery prefetches.
   *
   * @since 4.2
   */
  class FluentSelectPrefetchRouterAction implements PrefetchProcessor {
  
      FluentSelect<?, ?> query;
      QueryRouter router;
      EntityResolver resolver;
      ClassDescriptor classDescriptor;
  
      /**
       * Routes query prefetches, but not the query itself.
       */
      void route(FluentSelect<?, ?> query, QueryRouter router, EntityResolver resolver) {
          if (!query.isFetchingDataRows() && query.getPrefetches() != null) {
  
              this.query = query;
              this.router = router;
              this.resolver = resolver;
              this.classDescriptor = query.getMetaData(resolver).getClassDescriptor();
  
              query.getPrefetches().traverse(this);
          }
      }
  
      public boolean startPhantomPrefetch(PrefetchTreeNode node) {
          return true;
      }
  
      public boolean startDisjointPrefetch(PrefetchTreeNode node) {
          // don't do anything to root
          if (node == query.getPrefetches()) {
              return true;
          }
  
          CayennePath prefetchPath = node.getPath();
  
          // find last relationship
          Iterator<CayenneMapEntry> it = classDescriptor.getEntity().resolvePathComponents(prefetchPath);
  
          ObjRelationship relationship = null;
          while (it.hasNext()) {
              relationship = (ObjRelationship) it.next();
          }
  
          if (relationship == null) {
              throw new CayenneRuntimeException("Invalid prefetch '%s' for entity '%s'"
                      , prefetchPath, classDescriptor.getEntity().getName());
          }
  
          // chain query and entity qualifiers
          Expression queryQualifier = query.getWhere();
  
          Expression entityQualifier = classDescriptor
                  .getEntityInheritanceTree()
                  .qualifierForEntityAndSubclasses();
  
          if (entityQualifier != null) {
              queryQualifier = (queryQualifier != null)
                      ? queryQualifier.andExp(entityQualifier)
                      : entityQualifier;
          }
  
          // create and configure PrefetchSelectQuery
          PrefetchSelectQuery<?> prefetchQuery = new PrefetchSelectQuery<>(prefetchPath, relationship);
          prefetchQuery.statementFetchSize(query.getStatementFetchSize());
  
          prefetchQuery.where(classDescriptor.getEntity()
                  .translateToRelatedEntity(queryQualifier, prefetchPath));
  
          if (relationship.isSourceIndependentFromTargetChange()) {
              // setup extra result columns to be able to relate result rows to the parent result objects.
              prefetchQuery.addResultPath(ExpressionFactory.dbPathExp(relationship.getReverseDbRelationshipPath()));
          }
  
          // pass prefetch subtree to enable joint prefetches...
          prefetchQuery.setPrefetchTree(node);
  
          // route...
          prefetchQuery.route(router, resolver, null);
          return true;
      }
  
      public boolean startDisjointByIdPrefetch(PrefetchTreeNode prefetchTreeNode) {
          // simply pass through
          return true;
      }
  
      public boolean startJointPrefetch(PrefetchTreeNode node) {
          // simply pass through
          return true;
      }
  
      public boolean startUnknownPrefetch(PrefetchTreeNode node) {
          // don't do anything to root
          if (node == query.getPrefetches()) {
              return true;
          }
  
          // route unknown as disjoint...
          return startDisjointPrefetch(node);
      }
  
      public void finishPrefetch(PrefetchTreeNode node) {
      }
  }
  