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  package org.apache.cayenne.access.sqlbuilder.sqltree;
  
  import java.util.Map;
  import java.util.Optional;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.function.Function;
  
  import org.apache.cayenne.map.DbAttribute;
  
  /**
   * @since 4.2
   * @param <T> type of the node to process
   */
  public class PerAttributeChildProcessor<T extends Node> implements ChildProcessor<T> {
  
      private final Map<DbAttribute, ChildProcessor<T>> processorByAttribute = new ConcurrentHashMap<>();
      private final Function<T, DbAttribute> attributeMapper;
      private final Function<DbAttribute, ChildProcessor<T>> processorFactory;
  
      public PerAttributeChildProcessor(Function<T, DbAttribute> attributeMapper,
                                        Function<DbAttribute, ChildProcessor<T>> processorFactory) {
          this.processorFactory = processorFactory;
          this.attributeMapper = attributeMapper;
      }
  
      @Override
      public Optional<Node> process(Node parent, T child, int index) {
          DbAttribute dbAttribute = attributeMapper.apply(child);
          if(dbAttribute == null) {
              return processorFactory.apply(null).process(parent, child, index);
          }
          return processorByAttribute
                  .computeIfAbsent(dbAttribute, processorFactory)
                  .process(parent, child, index);
      }
  }
  