Can PDO methods fail and not throw PDOException?

Question

I'm tweaking a legacy database class written for PHP/5.2 that was designed to connect to MySQL and hide all errors. I've configured the PDO instance to throw exceptions:

 new PDO($dsn, $user, $pass, array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION))

Now I need to adjust my code accordingly to handle the case where functions can throw an exception where they wouldn't before so I head to the manual.

In some cases the manual is explicit, e.g. PDO::prepare:

If the database server successfully prepares the statement, PDO::prepare() returns a PDOStatement object. If the database server cannot successfully prepare the statement, PDO::prepare() returns FALSE or emits PDOException (depending on error handling).

In other cases it's kind of vague, e.g. PDO::commit:

Returns TRUE on success or FALSE on failure.
Throws a PDOException if there is no active transaction.

(Can it fail for some other reason and simply return false?)

And there're cases when exceptions are not even mentioned, e.g. PDO::bindValue:

Returns TRUE on success or FALSE on failure.

... even though it's clear to verify that it does throw PDOException on error (at least, on certain errors).

Do I still need to check the return value of methods that return false on error when the manual doesn't say otherwise?

Answer 1

No, when you set PDO::ERRMODE_EXCEPTION there will be always exception for any errors

Answer 2

When you have exceptions enabled and there is an error happening in your code, the code directly stops executing from that function, so it wont return anything.

So to be blund, you don't need to check the return values but if you don't you cannot error anything specific and you would rely fully on PDO to error correctly.

When I created my database system, I take advantage of both if I see an error upcoming, I throw it myself instead. For example $pdo->prepare('') is very much valid but will error upon binding.

Then there are other functions such as fetch that wont error if there are no results in the database, not checking the results from that would be silly.

Now for committing to fail, I believe there is 1 scenario that would cause it to return false without throwing an exception and that is when the connection to the server drops after connecting to the database and before calling PDO::commit, quite good to know if you have a remote database server.

So to answer your question, yes it can fail without throwing an exception, but its timing has to be very specific even more so if you have a local database.

Answer 3

Try this one

 try {
   $db = new PDO("mysql:host=localhost;dbname=dbname", "username", "password");
}catch( PDOException $Exception ) {  $Exception->getMessage( )  ;  }