This code works fine, but I'll want to handle exception if any thing goes wrong, so I deliberately made a syntax error in the query but nothing happens. Below is the code
try {
$sql = "INSERT INTO journals (topic, author, ) VALUES ('$topic', '$authors', ')";
echo "1st";
$lecturers_db->query($sql);
echo "second";
} catch(PDOException $e) {
echo $e->getMessage();
echo $msg = "Error!";
}
Without the obvious syntax error, the code works fine but with the syntax error, nothing happens, all the code in the try block executes and the code in the catch block never executes.
I want to raise an exception, please how do I do it here, thanks for any help.
Be sure to set the attribute PDO::ATTR_ERRMODE to PDO::ERRMODE_EXCEPTION, as soon as you init your pdo object:
$lecturers_db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
After that, any failed queries will raise an exception
Exceptions are thrown. Syntax errors in code != Exceptions.
<?php
try {
$code = 12;
throw new PDOException('Message', $code );
} catch (PDOException $e) {
}
?>
However, from the maual:
You should not throw a PDOException from your own code. See Exceptions
for more information about Exceptions in PHP.
My advice is to throw either a general exception, or to write your own custom exception to handle your error.
Related
I perfectly understand the nuances of the (try/throw/catch) block.
What I don't understand is:
If we gonna use an IF (or any control structure) inside our try block anyway in order to test if a condition is met, only then, 'throw' an exception if the results of that test is false, then... in my opinion: throw/generate an exception is useles; because if a condition is not met, we can simply print an error message, call a function, instantiate a class, redirect to another location, etc.
Another story would be, if for instance, a variable was not initialized, we enclose that variable inside a try{} block, echo the variable, and from that point onward, everything will be handle by the catch() block because the try block raises an error; and since the try/catch blocks talk each other, the catch block will catch every error that was originated from his corresponding try block. However, you can set a custom error message inside yout try block (optional).
What I've read so far:
every results from searching: if vs. try
I do see the difference.
But I can not understand why some people choose try/throw/catch over if...else...switch...while... etc.
As far I can see, try/throw/catch can be used for debugging, though.
One benefit of exceptions over if/then is that you can wrap try/catch around a large block of code. It will be triggered if an error happens anywhere in the block.
try {
$db = db_open();
$statement = $db->prepare($sql);
$result = $statement->execute($params);
} catch (Exception $e) {
die($e->getMessage());
}
With if/then, you would have to perform a test at each step.
$db = db_open();
if (!$db) {
die(db_connect_error());
}
$statement = $db->prepare($sql);
if (!$statement) {
die(db_error($db));
}
$result = $statement->execute($params);
if (!$result) {
die(db_error($db));
}
As you said, it's a lot of overhead to throw an exception inside a try/catch block and catch it immediately.
try {
if (...) {
// good, do no throw
} else {
throw new Exception();
}
} catch ($e) {
// handle exception
}
This should be replaced by:
if (...) {
// good
} else {
// handle error, no exception
}
Exceptions are useful because they bubble up. So imagine if you have this code instead:
function bla() {
try {
tryToDoSomething();
} catch ($e) {
// handle error
}
}
function tryToDoSomething() {
if ($somethingNotAvailable) {
throw new Exception();
}
doSomething();
}
In this case, the function that defines the try/catch is NOT the one throwing the exception. tryToDoSomething() does not know how to handle the errors so it will let parent methods to take care of it. The exception can bubble up the call stack until someone catches it and handles the error. That's how exceptions can actually be useful :)
This question already has answers here:
What to do with mysqli problems? Errors like mysqli_fetch_array(): Argument #1 must be of type mysqli_result and such
(2 answers)
Closed 2 years ago.
I started using OO-MySQLi after procedural MySQL and I have a problem.
In production environment my system displays all errors as a custom page.
MySQLi errors is an "error" too and I want catch them, but in documentation described only one way to do this:
if (!$mysqli->query("SET a=1")) {
exit('An error occurred: ' . $mysqli->error);
}
(just for example).
This is a very bad way, because in my system I'm doing many things when error occurred, like logging, calling events, etc.
Of course, I can extend mysqli class, for example:
class myMysqli {
public function __construct(/* ... */)
{
parent::__construct(/* ... */);
}
public function query(/* .. */)
{
parent::query(/* ... */);
if($this->errno !== 0)
{
// An error occurred
}
}
}
$mysqli = new myMysqli(/* ... */);
$mysqli->query(/* ... */);
But this way I need to extend almost ALL methods where error can occur.
Moreover, MySQLi provides prepared statements (mysqli_stmt class) that has its own errors!
Can you know a better way to handle MySQLi errors?
Thank you in advance.
Added
About exceptions:
Do I understand correctly that with exceptions I need do something like this:
try {
$mysqli->query(/* ... */);
} catch (Exception $e) {
// An error occurred
}
But this is similar to
if(!$mysqli->query(/* ... */))
{
// An error occured
}
What a difference?
First of all, your old approach was wrong.
exit('An error occurred: ' . $mysqli->error);
is a bad practice in general and shouldn't be used with mysqli as well.
What you really want is error/exception handler. Where you can do whatever things like logging, calling events, showing pages.
Exception is better than regular error - so, set your mysqli in exception mode as shown in other answer, and then catch all the errors in error handler. While try..catch have to be used only when you have a distinct particular action to handle the error.
I use the try...catch method like this...
try {
// get result of record from 'id'
$query = "SELECT * FROM models WHERE id =$id";
$result = $mysqli->query($query);
if (!$result) {
throw new Exception($mysqli->error());
}
$row = $result->fetch_array();
}
catch (Exception $e)
{
echo "We are currently experiencing issues. Please try again later.";
echo $e->getMessage();
}
finally
{
$result->free();
}
Does that help at all?
You use 'try' to test a condition and throw an exception if it returns true (!$result). And use 'catch' to catch everything else that might just happen!
I'm using the following script to use a database using PHP:
try{
$db = new PDO('mysql:host='.$host.';port='.$port.';dbname='.$db, $user, $pass, $options);
}
catch(Exception $e){
$GLOBALS['errors'][] = $e;
}
Now, I want to use this database handle to do a request using this code:
try{
$query = $db->prepare("INSERT INTO users (...) VALUES (...);");
$query->execute(array(
'...' => $...,
'...' => $...
));
}
catch(Exception $e){
$GLOBALS['errors'][] = $e;
}
Here is the problem:
When the connection to the DB is OK, everything works,
When the connection fails but I don't use the DB, I have the $GLOBALS['errors'][] array and the script is still running afterwards,
When the connection to the DB has failed, I get the following fatal error:
Notice: Undefined variable: db in C:\xampp\htdocs[...]\test.php on line 32
Fatal error: Call to a member function prepare() on a non-object in C:\xampp\htdocs[...]\test.php on line 32
Note: Line 32 is the $query = $db->prepare(...) instruction.
That is to say, the script crashes, and the try/catch seems to be useless. Do you know why this second try/catch don't works and how to solve it?
Thanks for the help!
EDIT: There are some really good replies. I've validated one which is not exactly what I wanted to do, but which is probably the best approach.
try/catch blocks only work for thrown exceptions (throw Exception or a subclass of Exception must be called). You cannot catch fatal errors using try/catch.
If your DB connection cannot be established, I would consider it fatal since you probably need your DB to do anything meaningful on the page.
PDO will throw an exception if the connection cannot be established. Your specific problem is that $db is not defined when you try to call a method with it so you get a null pointer (sort of) which is fatal. Rather than jump through if ($db == null) hoops as others are suggesting, you should just fix your code to make sure that $db is either always defined when you need it or have a less fragile way of making sure a DB connection is available in the code that uses it.
If you really want to "catch" fatal errors, use set_error_handler, but this still stops script execution on fatal errors.
In PHP7, we now can using try catch fatal error with simple work
try {
do some thing evil
} catch (Error $e) {
echo 'Now you can catch me!';
}
But usualy, we should avoid using catch Error, because it involve to miss code which is belong to programmer's reponsibility :-)
I will not report what has already been written about testing if $db is empty. Just add that a "clean" solution is to artificially create an exception if the connection to the database failed:
if ($db == NULL) throw new Exception('Connection failed.');
Insert the previous line in the try - catch as follow:
try{
// This line create an exception if $db is empty
if ($db == NULL) throw new Exception('Connection failed.');
$query = $db->prepare("INSERT INTO users (...) VALUES (...);");
$query->execute(array(
'...' => $...,
'...' => $...
));
}
catch(Exception $e){
$GLOBALS['errors'][] = $e;
}
Hope this will help others!
If database connection fails, $db from your first try .. catch block will be null. That's why later you cannot use a member of non-object, in your case $db->prepare(...). Before using this add
if ($db) {
// other try catch statement
}
This will ensure that you have db instance to work with it.
Try adding the following if statement :
if ($db) {
$query = $db->prepare("INSERT INTO users (...) VALUES (...);");
$query->execute(....);
}
else die('Connection lost');
try{
if(!is_null($db))
{
$query = $db->prepare("INSERT INTO users (...) VALUES (...);");
$query->execute(array(
'...' => $...,
'...' => $...
));
}
}
catch(Exception $e){
$GLOBALS['errors'][] = $e;
}
for the first time i came across try, throw catch statement in PHP, and i felt this could be the better way for handling errors as i was quite messing my error handlers with lots of if else statements, however as i am performing CRUD operations on my script i wanted my error handlers to perform two task.
display the user readable or
custom error message back to the
user.
catch all the error in a file for
me to read.
i am using the following code..
try
{
$name = filter_var($_POST['name'], FILTER_SANITIZE_STRING);
if($cname == $name)
{
throw new Exception('Sorry, Please Change the value to update ');
}
$sth = $dbh->prepare("UPDATE countries SET name = :name WHERE id = :cid");
$sth->bindParam(':name', $name);
$sth->bindParam(':cid', $cid);
$sth->execute();
}
catch(PDOException $e)
{
echo $e->getMessage();
file_put_contents("resources/logs/Connection-log.txt", DATE.PHP_EOL.$e->getMessage().PHP_EOL.PHP_EOL, FILE_APPEND);
}
if the condition $cname == $name is true i just want to display the error 'Sorry, Please Change the value to update, however this is not happening here, instead it throws the Fatal Error with this message.
Fatal error: Uncaught exception 'Exception' with message 'Sorry, Please Change the value to update ' in /Applications/MAMP/htdocs/kokaris/administrator/resources/library/models/countries.php:24 Stack trace: #0 /Applications/MAMP/htdocs/kokaris/administrator/location-manager.php(43): include() #1 {main} thrown in /Applications/MAMP/htdocs/kokaris/administrator/resources/library/models/countries.php on line 24
how do i achieve this?
thank you..
Your catch is catching a PDOException :
catch(PDOException $e)
While you are throwing a Exception :
throw new Exception('Sorry, P...
PDOException is a sub-class of Exception, which means that :
A PDOException is an Exception
But an Exception is not a PDOException.
So, when you are trying to catch a PDOException, your catch will not also catch Exception.
If you want your Exception to be catched, you must use something like this :
try {
}
catch (PDOException $e) {
// deal with PDOException
}
catch (Exception $e) {
// deal with all other kinds of exceptions
}
In this case, the catch PDOException can be avoided, if you do not want to do some special treatment for PDOExceptions, and just want all exceptions to be dealt with the same way :
try {
}
catch (Exception $e) {
// deal with all kinds of exceptions
}
You are throwing an Exception but catching a PDOException.
You should catch the same as you throw, so you might want to change your catch to:
catch(Exception $e)
Or if you also want to catch that PDOException and not do the file_put_contents for your own excpetion, add a catch for your specific Exception.
YOu could ofcourse also change your throw to PDOException, same thing basically.
I been searching for this and I just seem to run into the same articles, in this code:
try
{
//some code
}
catch(Exception $e){
throw $e;
}
Where does $e gets stored or how the webmaster see it? Should I look for a special function?
An Exception object (in this case, $e) thrown from inside a catch{} block will be caught by the next highest try{} catch{} block.
Here's a silly example:
try {
try {
throw new Exception("This is thrown from the inner exception handler.");
}catch(Exception $e) {
throw $e;
}
}catch(Exception $e) {
die("I'm the outer exception handler (" . $e->getMessage() . ")<br />");
}
The output of the above is
I'm the outer exception handler (This is thrown from the inner exception handler.)
One nice thing is that Exception implements __toString() and outputs a call stack trace.
So sometimes in low-level Exceptions that I know I'm gonna want to see how I got to, in the catch() I simply do
error_log($e);
$e is an instance of Exception or any other class that extended from Exception. Those objects have some specific attributes and methods in common (inherited from the Exception class) you can use. See the chapter about exceptions and the Exception member list for more details.
I'm assuming your using some sort of third party code/library with this code in it that is throwing the exception into your code. You simply have to be ready for an exception to be thrown to catch it, then you can log it/display it however you want.
try {
$Library->procedure();
catch(Exception $e) {
echo $e->getMessage(); //would echo the exception message.
}
For more information read the PHP manual's entry on Exceptions.
The lines:
catch(Exception $e){
throw $e;
}
Don\t make sense. When you catch an Exception you're suppose to do something with the exception like:
catch(Exception $e){
error_log($e->getMessage());
die('An error has occurred');
}
But in your case the Exception is thrown directly to an outer try-block which would already happen.
If you change your code to:
//some code
Would create the exact same behaviour.