Validating ISBNs using the new public API

Strict validation using the Isbn::validateAs… methods

The 2.3.0 update introduced three new validation methods:

• Isbn::validateAsIsbn10 ( string $value ) : void
• Isbn::validateAsIsbn13 ( string $value ) : void
• Isbn::validateAsEan13 ( string $value ) : void

These methods are the recommended way if you want to strictly assert that a string is a valid ISBN-10, ISBN-13 or EAN-13.

They throw exceptions if string passed as an argument:

• is parsable (and thus, can be converted to a valid ISBN) but does not match the excepted format,
• or if it can even be parsed at all.

Example:

$input = "9781234567890";

try {
  Isbn::validateAsIsbn13($input);
 	echo "ISBN $input is valid!";
} catch(Exception $e) {
  echo "ISBN $input is invalid!";
}

Parsability assertion using the isParsable method

The 2.4.0 update introduced a new method:

Isbn::isParsable ( string $value ) : boolean

This method returns true if the $value string can be parsed (and thus, converted into a valid ISBN-10, ISBN-13, EAN-13 or GTIN-14) and false if it cannot be.

Example usage:

$input = "978-2-84344-949-9";
if (Isbn::isParsable($input)) {
  $ean = Isbn::convertToEan13($input);
  echo "String $input was converted to EAN-13 $ean";
} else {
  echo "String $input was not converted because it is not parsable!";
}

Please note that Isbn::isParsable does not guaranty that $value is valid in any way, but only that it is parsable enough that it can be converted to a valid ISBN. This is a similar behavior to the legacy Isbn->isValid and Isbn->validate methods (deprecated in 2.3.0) but with a much less confusing name.

You don’t need to call Isbn::isParsable before trying to attempt to convert a string using one of the Isbn::convertAs… methods, unlike the legacy Isbn->format that required you to preventively call Isbn->isValid to avoid unexpected behavior. Now, you can just catch exceptions :

$input = "978-2-84344-949-9";
try {
  $ean = Isbn::convertToEan13($input);
  echo "String $input was converted to EAN-13 $ean";
} catch(Exception $e) {
  echo "String $input was not converted because it is not parsable!";
}
  

One reason to use Isbn::isParsable is if you want to validate parsability in a condition among others.

function searchFor(string $value) {
  if (Isbn::isParsable($value)) {
    $ean = Isbn::convertToEan13($value);
    searchByEan($ean);
  } elseif (is_numeric($value)) {
    searchById(int $value);
  } else {
    searchByKeyword($value);
  }
}

The above function would have been much less easy to read if it would have been implemented using try…catch.