The following try..catch is meant to run a method if it exists and run a different method if it doesn't..
$heading = new HeadingMan();
try {
if (!is_callable($heading->{$this->breadcrumbs->getCrumb(3)}())) {
throw new Exception ('<b>Error - HeadingMan class can not handle: </b>' . $this->breadcrumbs->getCrumb(3));
}
$heading->{$this->breadcrumbs->getCrumb(3)};
}
catch (Exception $e) {
$heading->latest();
}
However, the catch statement always triggers, and throws a new exception (runs the catch portion of the statement).
How do I check a method exists in a class by using a series of function calls
$this->breadcrumbs->getCrumb(3);
to get the name of the function.?
$bool = method_exists($class,$method);
http://php.net/manual/en/function.method-exists.php
Related
I am looking to get some advice on best practice for throwing exceptions and catching them. I am using a 3rd party library for connecting to Amazon mws API. This library already throws exceptions which I am catching within a function.
My question is, should this function pass the exception onto the main script by using a try-catch? e.g.
function myFunction() {
try {
$obj = new Object();
$obj->makeCall();
return $obj->getData();
} catch (Exception $ex) {
throw new Exception('There was a problem with the library '.$ex->getMessage());
}
}
then in the main script;
try {
//make the call
$response = myFunction();
} catch (Exception $e){
//log error
$logger->error("log error");
}
If you are catching the exception in the main script, you don't need to catch it in your function myFunction until you need to do some processing in your function.
The control will return to the exception being catched in the main script if any of it's children or children's children and so on throw an exception.
It's my first time to use DB::transaction() but how exactly does it work if a transaction fails or is successful? In the example below, do I have to manually assign a value to return true, or if it fails will the method either return false or totally exit the transaction (therefore skipping the rest of the code)? The docs aren't so helpful on this.
use Exception;
use DB;
try {
$success = DB::transaction(function() {
// Run some queries
});
print_r($success);
} catch(Exception $e) {
echo 'Uh oh.';
}
Solution
I wrote down this solution for others who might be wondering.
Since I was more concerned about returning a boolean value depending on the success of my query, with a few modifications it now returns true/false depending on its success:
use Exception;
use DB;
try {
$exception = DB::transaction(function() {
// Run queries here
});
return is_null($exception) ? true : $exception;
} catch(Exception $e) {
return false;
}
Take note that the variable $exception is never returned since if something goes wrong with your query, the catch is immediately triggered returning false. Thanks to #ilaijin for showing that an Exception object is thrown if something goes wrong.
By giving a look at function transaction it does its process inside a try/catch block
public function transaction(Closure $callback)
{
$this->beginTransaction();
// We'll simply execute the given callback within a try / catch block
// and if we catch any exception we can rollback the transaction
// so that none of the changes are persisted to the database.
try
{
$result = $callback($this);
$this->commit();
}
// If we catch an exception, we will roll back so nothing gets messed
// up in the database. Then we'll re-throw the exception so it can
// be handled how the developer sees fit for their applications.
catch (\Exception $e)
{
$this->rollBack();
throw $e;
}
So throws an Exception (after the rollback) if fails or returns $result, which is the result of your callback
There is a short version if you want to use the default transaction method that ships with Laravel without handling it manually.
$result = DB::transaction(function () {
// logic here
return $somethingYouWantToCheckLater;
});
You can also use the following
DB::rollback();
i have the following code and i'm wondering if i can use try & catch as below:
class fun_database implements idbInfo{
private $srvr=idbInfo::srvr_name;
private $usr=idbInfo::usrnm;
private $pass=idbInfo::psswrd;
private $db=idbInfo::db_name;
public function connct(){
$hookup = new mysqli($this->srvr, $this->usr, $this->pass, $this->db);
if ($hookup->connect_errno)
{
throw new Exception("Error Processing Request", 1);
}
}
public function sql_require_all($table_name, $table_col){
$hookup = new connct();
$result = $hookup->query("SELECT $table_col FROM $table_name");
if($hookup->error()){
throw new Exception("Error Processing Request", 1);
}
return $result->num_rows;
}
}
This is a simple connection to the mysql and performing some querying there. Here is and the actual call of the functions above:
$conn = new fun_database();
try{
$result = $conn->sql_require_all('wordtypes', 'types');
}
catch(Exception $err){
echo "Problems at:". $err->getMessage();
}
return "<option>".$result."</option>";
What i'm asking is a bit theory. Most probably this code is NOT WORKING (i didn't test it yet). I just want to know is it possible with one 'try' to 'catch' two exceptions (as you can see the first 'throw' is in the second method of fun_database, and the second 'throw' is in the first method of the same object which is only called from the second method).
sorry for making it too complicated but still can't figure it out id this structure of try/catch is working.
you can only catch different types of exception...
class fun_database implements idbInfo{
private $srvr=idbInfo::srvr_name;
private $usr=idbInfo::usrnm;
private $pass=idbInfo::psswrd;
private $db=idbInfo::db_name;
public function connct(){
$hookup = new mysqli($this->srvr, $this->usr, $this->pass, $this->db);
if ($hookup->connect_errno)
{
throw new DomainException("Error Processing Request", 1);
}
}
public function sql_require_all($table_name, $table_col){
$hookup = new connct();
$result = $hookup->query("SELECT $table_col FROM $table_name");
if($hookup->error()){
throw new Exception("Error Processing Request", 1);
}
return $result->num_rows;
}
}
Then:
try{
$conn = new fun_database();
$result = $conn->sql_require_all('wordtypes', 'types');
}
catch(DomainException $err){
echo "This Problem at:". $err->getMessage();
}
catch(Exception $err){
echo "That Problem at:". $err->getMessage();
}
return "<option>".$result."</option>";
you would need your class instantiation inside that try block though I believe.
It wouldn't catch the two exceptions because as soon as the first exception is thrown, it goes straight to the catch block, thereby skipping the second exception directly.
You could wrap each code which may throw an exception in its own try-catch block.
Yes and no. Your code is able to catch two of this exceptions but not both of them at the same time. When one of exception will be thrown, program execution will look for closest catch block, which fits to catch Exception class. Rest of code will be omitted.
You can throw an exception at an point in the program (not after an excpetion if it is not caught).
As soon as it hits this point it will stop and try to make the fallback to the a try catch block. As soon as it finds one it will do this block (if it is a good catch)
You could make a try catch around your entire program or just a function.
You can throw different classes of exceptions:
class ConnectException extends Exception {}
class QueryException extends Exception {}
and then catch different exceptions:
try {
// something
}
catch (ConnectException $ex) {
// connect exception
}
catch (QueryException $ex) {
// query exception
}
It is not possible because when you throw
throw new Exception("Error Processing Request", 1);
this exception it will be caught in this line
catch(Exception $err){
echo "This Problem at:". $err->getMessage();
}
you will not reach the line that can throw the other exception if first exception was thrown
I can't get my head around WHEN to throw and catch exceptions for when I call functions from classes.
Please imagine that my QuizMaker class looks like this:
// Define exceptions for use in class
private class CreateQuizException extends Exception {}
private class InsertQuizException extends Exception {}
class QuizMaker()
{
// Define the items in my quiz object
$quiz_id = null;
$quiz_name = null;
// Function to create a quiz record in the database
function CreateQuizInDatabase()
{
try
{
$create_quiz = // Code to insert quiz
if (!$create_quiz)
{
// There was an error creating record in the database
throw new CreateQuizException("Failed inserting record");
}
else
{
// Return true, the quiz was created successfully
return true;
}
}
catch (CreateQuizException $create_quiz_exception)
{
// There was an error creating the quiz in the database
return false;
}
}
function InsertQuestions()
{
try
{
$insert_quiz = // Code to insert quiz
if (!$insert_quiz)
{
// There was an error creating record in the database
throw new CreateQuizException("Failed inserting quiz in to database");
}
else
{
// Success inserting quiz, return true
return true;
}
}
catch (InsertQuizException $insert_exception)
{
// Error inserting question
return false;
}
}
}
... and using this code, I use the class to create a new quiz in the database
class QuizMakerException extends Exception {}
try
{
// Create a blank new quiz maker object
$quiz_object = new QuizMaker();
// Set the quiz non-question variables
$quiz_object->quiz_name = $_POST['quiz_name'];
$quiz_object->quiz_intro = $_POST['quiz_intro'];
//... and so on ...
// Create the quiz record in the database if it is not already set
$quiz_object->CreateQuizRecord();
// Insert the quiz in to the database
$quiz_object->InsertQuestions();
}
catch (QuizMakerException $quiz_maker_error)
{
// I want to handle any errors from these functions here
}
For this piece of code, I want to call a QuizMakerException if any of the functions don't perform what I want them to (at the moment they return TRUE or FALSE).
What is the correct way to go about catching when any of the functions in this code does not perform what I want them to? At the moment they simply return TRUE or FALSE.
Do I really have to put lots of if/else statements between calling each function, I thought that was the whole point in exceptions, they simply halt the execution of further statements within the try/catch?
Do I throw a QuizMakerException from within the catch of my functions?
What is the right thing to do?
Help!
Well typically in the function which throws the exception, say your InsertQuestions method, you don't want to catch any exceptions, you want to throw them or let ones occurring to "bubble up". Then your "controller" code can make the determination of how to handle the exception.
If your goal here is to halt if CreateQuizRecord fails I would wrap CreateQuizRecord and InsertQuestions each in their own try block.
One advantage of exceptions is they can tell you more than a simple bool pass/fail. Either extending your base exception into things like "Invalid_Parameter" and testing for specific exceptions or -less ideally- inferring from properties of the exception. You can nest your catch blocks to handle exceptions individually.
Do I throw a QuizMakerException from within the catch of my functions?
Yes. Typically your code under // Code to insert quiz would itself return an exception. Say if the Model failed to insert it might be raising a database exception. In which case you can let that database exception bubble up, or do what you sort of doing now and catch it simply to in turn throw another exception (kinda dumbs down your exceptions in a way, doing that though).
Do I really have to put lots of if/else statements between calling each function, I thought that was the whole point in exceptions, they simply halt the execution of further statements within the try/catch?
I look at it like this, each call which throws an exception and is followed by a subsequent call which depends on this one not throwing any exceptions, should be wrapped in a try block. Assuming you want to handle it gracefully, if you simply want it to error out and halt just don't handle the exception. You'll get an error and stack trace. Sometimes that is desirable.
You might want to change the structure a bit. Your class QuizMaker can become:
<?php
// Define exceptions for use in class
public class CreateQuizException extends Exception {}
public class InsertQuizException extends Exception {}
class QuizMaker()
{
// Define the items in my quiz object
$quiz_id = null;
$quiz_name = null;
// Function to create a quiz record in the database
function CreateQuizInDatabase()
{
try
{
$create_quiz = // Code to insert quiz
if (!$create_quiz)
{
// There was an error creating record in the database
throw new CreateQuizException("Failed inserting record");
}
else
{
// Return true, the quiz was created successfully
return true;
}
}
catch (Exception $create_quiz_exception)
{
// There was an error creating the quiz in the database
throw new CreateQuizException(
"Failed inserting record " .
$create_quiz_exception->getMessage()
);
}
}
function InsertQuestions()
{
try
{
$insert_quiz = // Code to insert quiz
if (!$insert_quiz)
{
// There was an error creating record in the database
throw new InsertQuizException("Failed inserting quiz in to database");
}
else
{
// Success inserting quiz, return true
return true;
}
}
catch (Exception $insert_exception)
{
// Error inserting question
throw new InsertQuizException(
"Failed inserting quiz in to database " .
$create_quiz_exception->getMessage()
);
}
}
}
Effectively, if you cannot insert the record correctly, you throw an Insert exception. If anything goes wrong with that block of code, you catch it and throw again an Insert exception. Same goes with the Create function (or any other ones you might have).
In the main block of code you can have:
try
{
// Create a blank new quiz maker object
$quiz_object = new QuizMaker();
// Set the quiz non-question variables
$quiz_object->quiz_name = $_POST['quiz_name'];
$quiz_object->quiz_intro = $_POST['quiz_intro'];
//... and so on ...
// Create the quiz record in the database if it is not already set
$quiz_object->CreateQuizRecord();
// Insert the quiz in to the database
$quiz_object->InsertQuestions();
}
catch (InsertQuizException $insert_exception)
{
// Insert error
}
catch (CreateQuizException $create_quiz_exception)
{
// Create error
}
catch (Exception $quiz_maker_error)
{
// Any other error
}
If you don't want to have the multiple catch block there, just keep the catch(Exception) one and then check in it the type of each exception thrown to specify the actions taken from there.
HTH
The best thing to do is to not have to thhrow exceptions in the first place.
Exceptions are thrown when the program crashes and they are not made to handle wrong output.
If your function returns anything (even its the wrong thing) it doesn't need an exception.
To answer your question, if it's necessaryto use a lot of ifs/elses then you must use them.
I am trying to understand what the best approach would be to handle Exceptions in the following scenario:
I have a class employee:
class employee extends person {
private $salary;
private $baseSalary = 6.5;
function __construct($f, $m, $l, $a,$fsalary=0){
if(!is_numeric($fsalary)){
throw new Exception("Age supplied is not a number", 114);
}
parent::__construct($f, $m, $l, $a);
$this->salary=$fsalary;
}
function GetDetails(){
return parent::GetName().
"<br/>".
$this->salary;
}
function __toString(){
return $this->GetDetails();
}
}
And using this:
try{
if(!$f = new employee("Sarah", "Sebastian", "Pira", "abc")){
throw new Exception();
}
else {
echo $f;
}
}
catch (Exception $e){
echo "<br/>";
echo var_dump($e);
}
Now I would think it would be a good idea to throw an exception in the class and then use just one catch block in all the scripts that would be using an employee object - But this doesn't seem to work - I need to have a try catch block within the class - Is this the correct way of looking at this?
Thanks
I think what you're saying is that you want to do something like this:
try {
class Employee extends Person {
// ...blah blah...
}
}
catch(Exception $e) {
// handle exception
}
...and then be able to insantiate it in other classes, without explicitly catching any exceptions:
// try { << this would be removed
$employee = new Employee();
// }
// catch(Exception $e) {
// (a whole bunch of code to handle the exception here)
// }
You can't do that, because then the try/catch block in the class will only catch any exceptions that occur when defining the class. They won't be caught when you try to instantiate it because your new Employee line is outside the try/catch block.
So really, your problem is that you want to be able to re-use a try/catch block in multiple places without re-writing the code. In that case, your best solution is to move the contents of the catch block out to a separate function that you can call as necessary. Define the function in the Employee class file and call it like this:
try {
$employee = new Employee();
$employee->doSomeStuff();
$employee->doMoreStuffThatCouldThrowExceptions();
}
catch(Exception $e) {
handle_employee_exception($e);
}
It doesn't get rid of the try/catch block in every file, but it does mean that you don't have to duplicate the implementation of the exception-handling all the time. And don't define handle_employee_exception as an instance method of the class, do it as a separate function, otherwise it will cause a fatal error if the exception is thrown in the constructor because the variable won't exist.
You should read more about Exceptions in PHP.
You can handle exceptions within the methods of the class, sure. But you should rethink how you want to do this and... why.
Good practice is also creating own exception class, so you are able to distinguish exceptions thrown by your module / class from the exceptions thrown by something else. It looks like that (see more):
class EmployeeModule_Exception extends Exception {}
and when it comes to throwing exception:
// the second parameter below is error code
throw new EmployeeModule_Exception('some message', 123);
Catching is similar, only the below example will catch only your module's exceptions:
try {
// some code here
} catch (EmployeeModule_Exception $e) {
// display information about exception caught
echo 'Error message: ' . $e->getMessage() . '<br />';
echo 'Error code: ' . $e->getCode();
}