How to determine which service to call

Question

I have modeled my application using multiple 'user' domain objects.

• Candidate
• Recruiter
• Administrator

Each entity extends from an AbstractUser implementing UserInterface.

interface UserInterface
{
    public function getEmail();
    public function setEmail($email);
    public function getPassword();
    public function setPassword($password);
}

They all have their own a services CandidateService, AdminService etc implementing UserServiceInterface

interface UserServiceInterface
{
   public function getUserByEmail();
}

My problem arises when I need to fetch a user by their email address (say PasswordResetService) I am unable to determine which service I should be calling as the email could be either of them. I am also using mongoDB so I cannot simply run a native query joining the 'tables'.

My current thought is that I have to inject each service into the PasswordResetService and call getUserByEmail() on each of them until I get my desired user.

class PasswordResetService
{
   public function getUserByEmail($email) 
   {
       $user = $this->userService->getUserByEmail($email);
       if ($user) return $user;

       $user = $this->recruiterService->getUserByEmail($email);
       if ($user) return $user;

       // etc ...
   } 
}

From a design perspective the above seems to me like a poor approach as should I add a new user 'type' I would need to update the password service also.

Is there a better way of achieving this?

Answer 1

I would approach this by having a top level UserService that doesn't care what type of user it's dealing with.

If it gets a request for a user by email, it can look up on the database which type of user is correct and delegate the request to the correct service. This may sound a little inefficient, but used with an appropriate query caching later it's actually fine.

Other methods that are passed a user object could perhaps use double dispatch to forward the request to the correct service object., thus eliminating the need to hit the database for these operations.