PHP Try Catch in Exception Handling

Question

I have a database class dbconnect.php, and processform.php. Inside dbconnect.php there is a method for connecting to the database.

If there's an error, how do I throw an exception? Where do I put the try catch block, in the processform.php? People say I shouldn't echo an error directly from inside the class. Here's an example:

    <?php

    // dbconnect.php

    class DbConnect
    {

        public function open_connection()
        {

            /* Should I do it like this? */
            $this->conn = PDO($dsn, $this->username, $this->password);
            if (!$this->conn) {
                throw new Exception('Error connecting to the database.');
            }

            /* Or like this */
            try {
                $this->conn = PDO($dsn, $this->username, $this->password);
            } catch (PDOException $e) {
                echo 'Error: ', $e->getMessage(), '<br>';
            }
       }
    ?>

    // processform.php

    <?php
        require_once 'dbconnect.php';
        $pdo = new DbConnect($host, $username, $password);
        try {
            $pdo->open_connection();
        } catch (PDOException $e) {
            echo 'Error connecting to the database.');
        }
    ?>

I really want to learn the correct way of implementing the try catch in my code.

Answer 1

You don't have to throw an exception manually, especially on a successful connect :-)

Instead you need to tell PDO that it needs to throw exceptions when something goes wrong and you can do that when you open your database connection:

$options = array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION);
$this->conn = new PDO($dsn, $this->username, $this->password, $options);

Now you can put everything in try / catch blocks but that is not even necessary; if you don't do that, php will show you unhandled exceptions complete with a stack trace when you don't catch them manually.

And when you decide you want to fine-tune your error handling for your visitors, you can set your own exception handler using set_exception_handler(). That way you can handle everything at one place instead of wrapping different sections in try / catch blocks. Should you prefer that of course.

Answer 2

In my practice, I prefer to catch exception in bottom. I mean, second way in your DbConnect.

You can output error message to error log. And return an error code to front-end. So the front-end knows how to tell users an error occours in a friendly way.

What's more, you can use global error handler such as set_error_handler/set_exception_handler to do this. Redirect to an error page when error occours.