未捕获的异常PDOException，即使语句在try / catch块中

Question

I have run into an unexpected fatal error while testing an app that uses my database utility class (see code below). Here is a rundown of the test that was performed:

1. a new product was added to the database
2. the new product was put on an order
3. an attempt was made to delete the new product (while it was still being used on an order)

Results:

• as expected, the foreign key constraint in the database prevented deletion of the product
• unexpectedly, the following fatal error was displayed -
  Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[23000]: [Microsoft][SQL Server Native Client 11.0][SQL Server]The DELETE statement conflicted with the REFERENCE constraint "FK_Orders_Products". The conflict occurred in database "AppTEST", table "dbo.Orders", column 'productID'.' in C:\xampp\htdocs\App\classes\utility\DB.php:140 Stack trace: ...
  
  Line 140 is $stmt->execute();, which is in the query() method in the code below.
  
  Forum posts describing similar errors called out prepending global classes with a backslash, which I did, but to no avail. Why is the fatal error occurring?

Here are the pertinent parts of my database utility class for this question:

namespace classes\utility;

use \PDO,
    \Exception,
    \PDOException;

class DB
{
    private $_pdo,          # stores PDO object when it's instantiated
            $_error,        # stores whether query failed or not
            $_results,      # stores dataset returned by query
            $_count = 0;    # stores number of data rows returned

    /*connect to database*/
    private function __construct()
    {
        try
        {
            $connection = new \PDO('sqlsrv:Server=' . DB_HOST . ';Database=' . DB_NAME);
            $connection->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);     //to capture error messages returned by db
            $this->setPdo($connection);
        }
        catch(\PDOException $e)
        {
            exit((DEBUGMODE) ? $e->getMessage() : 'There was a problem connecting to the database.');
        }
    }

    # generic query method - uses named placeholders for parameter binding
    private function query($sql, $parameters = [])
    {
        try
        {
            $this->setError(false);
            $stmt = $this->getPdo()->prepare($sql); //assign to a variable with a short name
            if ($stmt):             
                if (count($parameters)):
                    foreach($parameters as $name => $parameter):
                        $stmt->bindValue(':'.$name, $parameter);                        
                    endforeach;
                endif;              
                $stmt->execute();
                $this->setCount($stmt->rowCount());
                if ($stmt->rowCount() == -1):       //conditionally do the following if SQL stmt was a SELECT
                    $this->setResults($stmt->fetchAll(\PDO::FETCH_OBJ));
                    $this->setCount($stmt->rowCount()); //overwrite count attribute with number of rows returned by SELECT stmt
                endif;
            endif;
            return $this;
        }
        catch (\PDOException $e)
        {
            $this->setError(true);
            throw $e;
        }
    }

    // setter and getter methods for private variables not shown

}

EDIT: Here is the code that calls the query() method. This method is also part of the DB class.

public function runQuery($operation, $sql, $parameters)
{       
    try
    {
        $this->query($sql, $parameters);                        //call query method all $operation types (read, write)
        if ($operation == 'read'):          
            if ($this->getCount()):
                if ($this->getCount() > 1):                     //for "read all"
                    $data = $this->getResults();
                else:                                           //for "read one"
                    $data = $this->getFirstResult();
                endif;
                $data = Arr::objectToArray($data);
                return $data;
            else:
                throw new \Exception("No data to display.");        //throw an exception if query runs fine but returns zero rows
            endif;
        endif;
    }
    catch (\PDOException $e)
    {
        throw (DEBUGMODE) ? $e : new \Exception("A database error occurred.  The $operation operation failed.");
    }
}

Answer 1

The problem turned out to be missing a backslash in a calling method. I had prepended the backslash in all references to global classes in the DB class, but not in other classes in other namespaces that had catch blocks.

There were actually 2 different ways to resolve this problem.
One approach was to change catch (Exception $e) to catch (\Exception $e).
Alternatively, leaving catch (Exception $e) as-is throughout the code and adding use \Exception; after the namespace declaration and before the class definition worked as well.