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  package org.apache.cayenne.exp.parser;
  
  import java.io.IOException;
  
  import org.apache.cayenne.ObjectContext;
  import org.apache.cayenne.Persistent;
  import org.apache.cayenne.access.translator.select.FluentSelectWrapper;
  import org.apache.cayenne.access.translator.select.TranslatableQueryWrapper;
  import org.apache.cayenne.exp.Expression;
  import org.apache.cayenne.query.FluentSelect;
  
  /**
   * @since 4.2
   */
  public class ASTSubquery extends SimpleNode {
  
      private final TranslatableQueryWrapper query;
  
      public ASTSubquery(FluentSelect<?, ?> query) {
          this(new FluentSelectWrapper(query));
      }
  
      public ASTSubquery(TranslatableQueryWrapper query) {
          super(0);
          this.query = query;
      }
  
      @Override
      protected String getExpressionOperator(int index) {
          throw new UnsupportedOperationException();
      }
  
      @Override
      protected Object evaluateNode(Object o) {
          ObjectContext context;
          if(o instanceof Persistent) {
              context = ((Persistent) o).getObjectContext();
          } else {
              throw new UnsupportedOperationException("Can't evaluate subquery expression against non-persistent object");
          }
  
          return context.select(query.unwrap());
      }
  
      @Override
      public Expression shallowCopy() {
          return new ASTSubquery(query);
      }
  
      @Override
      public int getType() {
          return Expression.SUBQUERY;
      }
  
      @Override
      public void appendAsString(Appendable out) throws IOException {
          out.append("EXISTS");
      }
  
      public TranslatableQueryWrapper getQuery() {
          return query;
      }
  
  }
  