异常处理的最佳实践：PDO + 控制器和存储库

Question

I've searched around for best practices on using exception handling with PDO, but most examples only look at it from a simple one class approach.

If I'm using controllers and a repo in an ORM type model, where should the various try/catch, and throw blocks happen?

A simplified example:

CONTROLLER: (creates repo object, fires off the loadProduct method, and loads the template)

class ProductController {
    public function viewProduct($product_id) {
        $ProductRepository = new ProductRepository($this->Pdo);
        $Product = $ProductRepository->loadProduct($product_id);
            
        include(__DIR__.'/../templates/product_template.php');
    }
}

MODEL/REPOSITORY:

class ProductRepository
{
    private $Pdo;
        
    public function __construct(PDO $Pdo)
    {
        $this->Pdo = $Pdo;
    }
            
    public function loadProduct($product_id,$withimages=0)
    {
        $Stm = $this->Pdo->prepare('
            SELECT p.product_id,p.model,p.price,p.prodinfo,pi.image_path
            FROM products p LEFT JOIN product_images pi
            ON p.product_id = pi.product_id
            WHERE p.product_id = :product_id
            AND pi.is_primary = 1
        ');
        $Stm->bindParam(':product_id',$product_id,PDO::PARAM_INT);
        $Stm->execute();
    
        return $this->arrayToObject($Stm->fetch(PDO::FETCH_ASSOC));    
    }
}

Should the try/catch blocks be put in the controller, and throw the exception if execute() returns nothing? Throw a separate exception if the $Pdo->prepare() method doesn't fire?

Answer 1

In general, exceptions handling policy is very simple. Especially with PDO. Because PDO throws one only in case of serious malfunction and there is little sense in continuing execution - so, just a default halt is okay.

So, for the average part of code, be it model, repository or whatever, no dedicated handling required at all.

Only in certain places for which you have a scenario for the failed query, try-catch have to be used. Most used scenario is a transaction rollback. So, if you have transaction, you may wish to wrap it in try and then rollback in catch.

To answer a clarification in comments:

That's two essentially different scenarios:

• There is nothing exceptional if SELECT can't find a product.
• While if INSERT somehow creates an invalid SQL query, it's indeed a catastrophe.

and they need different handling.

For the first case you don't need no exceptions at all, it's regular behavior. Just have in your template a branch that says "Nothing found"

For the second one, create a custom exception handler, that logs error, sends 503, and shows generic 503 error page.