public function prefix($field, $value)
    {
        if(!$value instanceof Expr\ConditionalExpression) {
            $value = $this->buildPart(Expr\TextComparisonExpression::escapeString((string)$value) . Expr\TextComparisonExpression::WILDCARD_STRING);
        }
        return new Expr\TextComparisonExpression($field,  $value, Expr\TextComparisonExpression::MATCH);
    }