PHP PDO execute() .... somewhat confused ?

[mat21]

Hi,

Below i have some sample code and am confused over execute(), i have the code below in a try and catch block, in the catch block i call a function i created to log any error that is caught in catch block to a .txt file.

I then looked online and it seems that i should do an if statement check on execute to ensure it executed the query, the part that confuses me if the execute failed i thought it would be caught in the catch block but it seems that is not the case.

To explain better i have commented the code in depth on the area that i am confused about.

Any help in making me understand would be great. I have not included all code above try and catch to keep things simple

<?php

try {
		// connect to database
		$dbh = sql_con();

	// checke if username exists on users table or users banlist table
	$stmt = $dbh->prepare("
	SELECT
	  users.user_login
	FROM
	  users
	WHERE
	  users.user_login = ?
	UNION ALL
	SELECT
	  users_banlist.user_banlist
	FROM
	  users_banlist
	WHERE
	  users_banlist.user_banlist = ?");

	// this is the part i am confused with, why is it i would use an if statement on execute() ?
	// i thought using a try and catch block any errors would be caught in the catch block.
	// using an if statement to check if execute() worked, i thought if execute failed it would
	// be handled by the catch block, i mean in my exmaple code here, what could cause the execute to fail ?
	// and why if execute failed it would not be caught by catch block ?
	// i am looing at exmaple online and i am reading different things and its all confusing me


	// execute query
	if(!$stmt->execute(array($username, $username))){
		echo 'something went wrong .. ';
	} else {
		// execute worked
		}
} // if any errors found log them  in my ExceptionErrorHandler() function and display friendly message
catch (PDOException $e) {
	// this function catches an error and logs them to file
	ExceptionErrorHandler($e);
	require_once($footer_inc);
	exit;
}
}

?>

Thanks or any help!

[NogDog]

$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

[mat21]

Hi,

Thanks for replying. I already have it set to the following in my sql_con() function which establishes connection to database:

$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

My confusion is in my try block i try to check if a username exists on the users table and user ban list table, it then gets executed using execute(), now my confusion is why would i use an if statement around the execute() as shown in my code ?

I thought if the execute() failed it would be caught in the catch block, but seeing examples online i see people wrap the execute() in an if statement as illustrated in my code.

and back to my questions:

1) In example code, why is it i would use an if statement on execute() ? (if it failed to execute shouldn't it be caught in the catch block ? )

2) What could cause the execute to fail ?

3) and why if execute failed it would not be caught by catch block ?

I am confusing myself somewhere and am not quite getting it, hence my questions.

Basically anything caught in the catch block in example code is written to a log file, in example code in catch block i call my function ExceptionErrorHandler($e);, this function writes any error to file.

Hopefully i have explained better.

Thanks for trying to help.

[NogDog]

Looks like it's because the default behavior for MySQL is to emulate prepared statements, which then seems to short-circuit the error-to-exception process. You can tell it not to do this, though it may cost some in terms of performance:

<?php
try {
	$dbh = new PDO('mysql:dbname=test;host=localhost', 'foo', 'bar');
	$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
// this line:
	$dbh->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
	echo "<p>Test 1:</p>\n";
	$sql = "SELECT 'foo'";
	$stmt = $dbh->prepare($sql);
	$stmt->execute();
	echo "<p>Test 2:</p>\n";
	$sql = "SELECT * FROM bogus_table_name";
	$stmt = $dbh->prepare($sql);
	$stmt->execute($sql);
}
catch(PDOException $e) {
	echo "<pre>".print_r($e, 1)."</pre>";
}