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  package org.apache.cayenne.exp.parser;
  
  import java.util.Collection;
  import java.util.Map;
  
  /**
   * Base class for all aggregation functions expressions
   * It's more like marker interface for now.
   * @since 4.0
   */
  public abstract class ASTAggregateFunctionCall extends ASTFunctionCall {
  
      ASTAggregateFunctionCall(int id, String functionName) {
          super(id, functionName);
      }
  
      ASTAggregateFunctionCall(int id, String functionName, Object... nodes) {
          super(id, functionName, nodes);
      }
  
      @Override
      protected int getRequiredChildrenCount() {
          return 0;
      }
  
      @Override
      protected Object evaluateNode(Object o) throws Exception {
          int len = jjtGetNumChildren();
          if(len == 0) {
              throw new UnsupportedOperationException("Aggregate functions can be calculated only for Collection or Map.");
          }
  
          Object firstChild = evaluateChild(0, o);
          Collection<?> values;
          if(firstChild instanceof Map) {
              values = ((Map<?, ?>) firstChild).values();
          } else if (firstChild instanceof Collection) {
              values = (Collection<?>) firstChild;
          } else {
              throw new UnsupportedOperationException("Aggregate functions can be calculated only for Collection or Map.");
          }
  
          return evaluateCollection(values);
      }
  
      protected Object evaluateCollection(Collection<?> values) {
          throw new UnsupportedOperationException("In-memory evaluation of aggregate functions not implemented yet.");
      }
  
      @Override
      protected Object evaluateSubNode(Object o, Object[] evaluatedChildren) throws Exception {
          throw new UnsupportedOperationException("In-memory evaluation of aggregate functions not implemented yet.");
      }
  }
  