Exceptions

Nette Database uses an exception hierarchy. The base class is Nette\Database\DriverException, which extends PDOException and provides enhanced functionality for working with database errors:

• The getDriverCode() method returns the error code from the database driver.
• The getSqlState() method returns the SQLSTATE code.
• The getQueryString() and getParameters() methods allow retrieving the original query and its parameters.

The DriverException class is extended by the following specialized exceptions:

• ConnectionException – indicates a failure to connect to the database server.
  • ConnectionLostException .{data-version:3.2.9} – the connection was dropped during an operation (server restart, network failure, idle timeout); a reconnect is required before further use.
• ConstraintViolationException – the base class for database constraint violations, from which the following exceptions inherit:
  • ForeignKeyConstraintViolationException – violation of a foreign key constraint.
  • NotNullConstraintViolationException – violation of a NOT NULL constraint.
  • UniqueConstraintViolationException – violation of a uniqueness constraint.
  • CheckConstraintViolationException .{data-version:3.2.9} – violation of a CHECK constraint.
• DeadlockException .{data-version:3.2.9} – a deadlock or serialization failure detected by the server; the transaction was rolled back and may be retried.
• LockTimeoutException .{data-version:3.2.9} – a lock-wait timeout was exceeded; the statement was aborted, but the surrounding transaction typically remains open.

The following example demonstrates how to catch a UniqueConstraintViolationException, which occurs when trying to insert a user with an email that already exists in the database (assuming the email column has a unique index):

try {
	$database->query('INSERT INTO users', [
		'email' => 'john@example.com',
		'name' => 'John Doe',
		'password' => $hashedPassword,
	]);
} catch (Nette\Database\UniqueConstraintViolationException $e) {
	echo 'A user with this email already exists.';

} catch (Nette\Database\DriverException $e) {
	echo 'An error occurred during registration: ' . $e->getMessage();
}