@Override
 public void readFields(DataInput input) throws IOException {
   super.readFields(input);
   accessor = new RowKeyValueAccessor();
   accessor.readFields(input);
   fromType = type; // fromType only needed on client side
 }
 public void visit(ColumnExpression entity) {
   wGetVisitor1().visit(entity.getExpression());
   wGetVisitor1().visit(entity.getAlias());
 }
 @Override
 public void write(DataOutput output) throws IOException {
   super.write(output);
   accessor.write(output);
 }