Editing of an existing object should be done in repository layer or in service?

Question

For example if I have a User that has debt. I want to change his debt. Should I do it in UserRepository or in service for example BuyingService by getting an object, editing it and saving it ?

Answer 1

You should leave the responsibility of mutating an object to that same object and use the repository to retrieve this object.

Example situation:

class User {
 private int debt; // debt in cents
 private string name;

 // getters

 public void makePayment(int cents){
  debt -= cents;
 }
}

class UserRepository {
 public User GetUserByName(string name){
  // Get appropriate user from database
 }
}

Usage (Jack pays 10€):

userRepository.GetUserByName("Jack").makePayment(1000);

Keep in mind that this is just an example approach. There is not one set way in programming to achieve something, you could very well do this entirely different.