Error & Exception Handling

Try-catch blocks, custom exceptions, error handlers og Throwable hierarchy i moderne PHP

Kategori: Fundamentals

🎯 Key Points

✓try-catch-finally - Struktureret exception handling med cleanup i finally block
✓Throwable interface - Root interface for både Exception og Error classes (PHP 7+)
✓Exception hierarchy - Custom exceptions der extender base Exception class
✓Error class - Catchable errors som TypeError, DivisionByZeroError (PHP 7+)
✓Custom exceptions - Domain-specific exception classes med custom properties og methods
✓set_exception_handler() - Global exception handler for uncaught exceptions
✓set_error_handler() - Convert PHP errors (warnings, notices) til exceptions
✓finally block - Kode der altid eksekveres uanset om exception blev kastet
✓throw keyword - Kast exceptions for at signalere error conditions
✓Multiple catch blocks - Catch forskellige exception types med forskellig handling
✓Exception chaining - Previous exception parameter for nested error context
✓SPL exceptions - Built-in exception types som InvalidArgumentException, RuntimeException

💻 Kode Eksempel

<?php

// Custom exception hierarchy
class DatabaseException extends Exception {}
class ConnectionException extends DatabaseException {}
class QueryException extends DatabaseException {
    public function __construct(
        string $message,
        private string $query,
        int $code = 0,
        ?Throwable $previous = null
    ) {
        parent::__construct($message, $code, $previous);
    }
    
    public function getQuery(): string {
        return $this->query;
    }
}

// Database class with proper error handling
class Database {
    private ?PDO $connection = null;
    
    public function connect(string $dsn): void {
        try {
            $this->connection = new PDO($dsn);
            $this->connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        } catch (PDOException $e) {
            throw new ConnectionException(
                "Failed to connect to database: {$e->getMessage()}",
                (int)$e->getCode(),
                $e
            );
        }
    }
    
    public function query(string $sql): array {
        if (!$this->connection) {
            throw new ConnectionException('Not connected to database');
        }
        
        try {
            $stmt = $this->connection->query($sql);
            return $stmt->fetchAll(PDO::FETCH_ASSOC);
        } catch (PDOException $e) {
            throw new QueryException(
                "Query failed: {$e->getMessage()}",
                $sql,
                (int)$e->getCode(),
                $e
            );
        }
    }
}

// Usage with multiple catch blocks
try {
    $db = new Database();
    $db->connect('sqlite::memory:');
    
    // This will fail - invalid SQL
    $results = $db->query('INVALID SQL');
    
} catch (ConnectionException $e) {
    echo "Connection error: {$e->getMessage()}\n";
    // Handle connection errors specifically
    
} catch (QueryException $e) {
    echo "Query error: {$e->getMessage()}\n";
    echo "Failed query: {$e->getQuery()}\n";
    
    // Check if there's a previous exception
    if ($prev = $e->getPrevious()) {
        echo "Caused by: {$prev->getMessage()}\n";
    }
    
} catch (DatabaseException $e) {
    echo "General database error: {$e->getMessage()}\n";
    
} finally {
    echo "Cleanup completed\n";
}

// Custom error handler to convert errors to exceptions
set_error_handler(function($severity, $message, $file, $line) {
    throw new ErrorException($message, 0, $severity, $file, $line);
});

try {
    // This warning will become an exception
    $result = 10 / 0; // Division by zero warning
} catch (ErrorException $e) {
    echo "Caught error as exception: {$e->getMessage()}\n";
}

restore_error_handler();

💼 Hvornår bruges det?

•API error responses hvor exceptions mappes til HTTP status codes og JSON error payloads
•Database operations hvor connection failures, query errors og transaction rollbacks håndteres
•File operations hvor missing files, permission errors og disk full scenarios catches gracefully
•External API calls hvor network timeouts, invalid responses og rate limits triggerer exceptions
•Form validation hvor ValidationException samler alle validation errors til user feedback
•Payment processing hvor PaymentException håndterer declined cards, insufficient funds og gateway errors

⭐ Best Practices

✓Create custom exception hierarchies for domain-specific errors - gør det lettere at catch specifikt
✓Always catch most specific exceptions first - rækkefølge matters i multiple catch blocks
✓Use finally blocks for cleanup operations (close files, connections) der skal ske uanset hvad
✓Log exceptions med context - message, stack trace, request data for debugging production issues
✓Never catch Throwable unless du re-throws - catching alt kan skjule critical errors
✓Include previous exception i custom exceptions for full error chain og debugging context
✓Throw exceptions for exceptional conditions only - ikke til normal control flow
✓Use SPL exceptions når muligt - InvalidArgumentException, RuntimeException etc frem for generic Exception

ℹ️ Quick Info

Kategori

Fundamentals

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