while learning DDD and cqrs, here is something I need to clarify. In a shopping context, I have a customer which I believe is my aggregate root and I would like to implement the simple use-case of change customer name.
Here is my implementation take on this using DDD/CQRS as much as I know.
My concerns are
- for validation, should the command also validate the input to make it conform with the value object or is it okay to leave it to handler?
- is my overall flow alright or am I heavily missing somewhere?
- If this flow is right, I see that Customer Aggregate root will be a huge class with numerous functions like changeName, changeAddress, changePhoneNumber, deleteSavedPaymentMethod and so on. It will become a god class, and that seems a bit odd to me, is it actually the right way of DDD aggregate root implementation?
// Value Object
class CustomerName
{
private string $name;
public function __construct(string $name)
{
if(empty($name)){
throw new InvalidNameException();
}
$this->name = $name;
}
}
// Aggregate Root
class Customer
{
private UUID $id;
private CustomerName $name;
public function __construct(UUID $id, CustomerName $name)
{
$this->id = $id;
$this->name = $name;
}
public function changeName(CustomerName $oldName, CustomerName $newName) {
if($oldName !== $this->name){
throw new InconsistencyException('Probably name was already changed');
}
$this->name = $newName;
}
}
// the command
class ChangeNameCommand
{
private string $id;
private string $oldName;
private string $newName;
public function __construct(string $id, string $oldName, string $newName)
{
if(empty($id)){ // only check for non empty string
throw new InvalidIDException();
}
$this->id = $id;
$this->oldName = $oldName;
$this->newName = $newName;
}
public function getNewName(): string
{
return $this->newName; // alternately I could return new CustomerName($this->newName)] ?
}
public function getOldName(): string
{
return $this->oldName;
}
public function getID(): string
{
return $this->id;
}
}
//the handler
class ChangeNameHandler
{
private EventBus $eBus;
public function __construct(EventBus $bus)
{
$this->eBus = $bus;
}
public function handle(ChangeNameCommand $nameCommand) {
try{
// value objects for verification
$newName = new CustomerName($nameCommand->getNewName());
$oldName = new CustomerName($nameCommand->getOldName());
$customerTable = new CustomerTable();
$customerRepo = new CustomerRepo($customerTable);
$id = new UUID($nameCommand->id());
$customer = $customerRepo->find($id);
$customer->changeName($oldName, $newName);
$customerRepo->add($customer);
$event = new CustomerNameChanged($id);
$this->eBus->dispatch($event);
} catch (Exception $e) {
$event = new CustomerNameChangFailed($nameCommand, $e);
$this->eBus->dispatch($event);
}
}
}
//controller
class Controller
{
public function change($request)
{
$cmd = new ChangeNameCommand($request->id, $request->old_name, $request->new_name);
$eventBus = new EventBus();
$handler = new ChangeNameHandler($eventBus);
$handler->handle($cmd);
}
}
PS. some classes like UUID, Repo etc skipped for brevity.
