QSqlRelationalTableModel displaying an icon instead of data

I'm displaying a table that contains one column with a blob (pdf file). I could have hide the column for the user, but instead i wanted to show a icon in the column when it was a document on file. I subclassed QsqlRealtionalTableModel and overload the data function. Shown below. My problem is that now the icon is showing along with the garbled data from the PDF. I thought that this overload function was substituting the icon for the data.

QVariant RelationalTableModelWithIcon::data(const QModelIndex &item, int role) const
{
  if(item.column() == 3 && role == Qt::DecorationRole)
    {
      QSqlRecord r= record(item.row());
      QByteArray a= r.field(3).value().toByteArray();
      QIcon icon = QIcon(":/icons/Art/Icons/Iynque-Flat-Ios7-Style-Documents-Pdf.ico");
      if(a.isNull() == false)
        {
          return QVariant(icon);
        }
    }
  return QSqlRelationalTableModel::data(item,role);
}

DROP TABLE IF EXISTS `ComOper`.`documentsqueue` ;

CREATE TABLE IF NOT EXISTS `ComOper`.`documentsqueue` (
  `iddocumentsqueue` INT NOT NULL AUTO_INCREMENT,
  `iddocument` INT NULL DEFAULT 1,
  `name` VARCHAR(45) NOT NULL,
  `image` MEDIUMBLOB NULL,
  `dateEntered` DATE NULL,
  `dateExpired` DATE NULL,
  `dateApproved` DATE NULL,
  `notes` MEDIUMTEXT NULL,
  `archived` TINYINT NULL DEFAULT 0,
  `iddocType` INT NOT NULL DEFAULT 1,
  `idsupplier` INT NOT NULL,
  `idfacilities` INT NOT NULL DEFAULT 1,
  `idproducts` INT NOT NULL DEFAULT 1,
  `iduser` INT NOT NULL DEFAULT 1,
  PRIMARY KEY (`iddocumentsqueue`),
  CONSTRAINT `fk_documentsqueue_docType1`
    FOREIGN KEY (`iddocType`)
    REFERENCES `ComOper`.`docType` (`iddocType`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_documentsqueue_documents1`
    FOREIGN KEY (`iddocument`)
    REFERENCES `ComOper`.`documents` (`iddocument`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_documentsqueue_user1`
    FOREIGN KEY (`iduser`)
    REFERENCES `ComOper`.`user` (`iduser`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_documentsqueue_products1`
    FOREIGN KEY (`idproducts`)
    REFERENCES `ComOper`.`products` (`idproducts`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_documentsqueue_facilities1`
    FOREIGN KEY (`idfacilities`)
    REFERENCES `ComOper`.`facilities` (`idfacilities`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_documentsqueue_supplier1`
    FOREIGN KEY (`idsupplier`)
    REFERENCES `ComOper`.`supplier` (`idsupplier`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)

So that you do not show the unreadable text of the PDF you must return an empty string when they ask for the Qt::DisplayRole role and return the icon when they ask for the Qt::DecorationRole role. I also recommend reading the icon once only if it is unique, which I show below:

*.h

private:
    QIcon icon;

*.cpp

RelationalTableModelWithIcon::RelationalTableModelWithIcon(QObject *parent, QSqlDatabase db):
    QSqlRelationalTableModel(parent, db)
{
    icon =  QIcon(":/icons/Art/Icons/Iynque-Flat-Ios7-Style-Documents-Pdf.ico");
}
QVariant RelationalTableModelWithIcon::data(const QModelIndex &index, int role) const
{
    if(index.column() == 3){
        if(role == Qt::DisplayRole)
            return "";
        else if ( role == Qt::DecorationRole)
            return icon;
    }
    return QSqlRelationalTableModel::data(index, role);
}