try-catch inside or around the function & use try-catch on each query execution or not?

Question

I have read several threads on stackoverflow about these questions:

1. Should I use try-catch inside or around the 'query' function?
2. Should I use try-catch on each query execution or not?

And, to be honest, I'm not sure I understand the answers - someone says yes, someone says no. So, I want to give practical example of how I do... and if you could give me answers to these two questions.

database.php:

try {
    $connection= new PDO(DB_DNS, DB_USER, DB_PASS);
    $connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch(Exception $e) {
    echo "Error: ".$e->getMessage();
    die();
}

user.php:

class User {
    public function pronadjiSveUsere() {
        global $connection;
        $sql= $connection->prepare("SELECT * FROM users");
        $result = $sql->execute();
        return $result ;
    }

    public function find_by_id($id=0) {
        global $connection;
        $sql= $connection->prepare("SELECT * FROM users WHERE id = :id");
        $result = $sql->execute(array($id));
        return $result->fetch(PDO::FETCH_OBJ);   
    }
}

As you can see - Class user has two methods. My questions are:

1. Should I use try-catch at all in these cases? 2. If the answer is yes - should I put within methods, for example:

    public function find_by_id($id=0) {
        try {
            global $connection;
            $sql= $connection->prepare("SELECT * FROM users WHERE id = :id");
            $result = $sql->execute(array($id));
            return $result->fetch(PDO::FETCH_OBJ);
        } catch(Exception $e) {
            echo $e->getMessage();
            die();
        }
    }

or around, whenever I'm use these methods, for example:

try {
    user->find_by_id($id);
} catch(Exception $e) {
    echo $e->getMessage();
    die();
}

Thank you in advance!

Answer 1

You can write books on that topic. In fact I believe there are books about this topic. So I'll keep it very brief.
For all your code snippets I'd say no - with a possible exception for the last one.
First one: database.php should not make the decision whether to go on or not. So the catch/die block might even be considered evil. Esp. when unconditionally printing the "real" error message. Some upper layer might want to try another connection instead. Or print a fancier "sorry, something went wrong. We're trying our best to bring back yaddayadda" message. Or do what it can without the database. (Maybe that's possible. It's not if database.php lets the php instance die).
Same argument for your class user. Unless there's something (intelligent) the code within user can do about the exception it should keep away from handling it. [ Printing the error message + die is not handling the exception ].
Again, it's rather unlikely (though not impossible) that the methods themselves can reasonably mitigate the problem - so, stay away from the exception; some other, upper layer has to deal with it anyway.

So, handle the execpetion only if you can really handle it.
edit: But at times it's a good idea to "convert" the actual exception into something the upper layer(s) are interested in. Then you would have a catch block that not really handles the exception but builds a new one (if possible including the original exception) and throws it.

Answer 2

If you need to stop the application every time your query fails and throws Exception - try to use php function set_exception_handler and remove all of your try...catch blocks for PDO in code. This function register global handler for all uncaught exception. But For example

<?php
    set_exception_handler(function ($e) {
        // Processing only PDOExceptions
        if ($e instanceof PDOException) {
            echo $e->getMessage();
            die();
        } else {
            throw $e;//do not process other exceptions
        }
    });
    ?>

This function you need to call before any of Sql queries.