Return response from controller or raise exception from service

Question

I need some guidance on how to send error responses to client from WebAPI controller for an update operation. I need to check if data is changed and if it has duplicate data. I have service class that does database operations.

Below is psuedo code

Approach 1

CustomerController.cs

public Task<IActionResult> UpdateCustomer(int id, Customer request)
{
     var customer = service.GetCustomer(id);

     if(customer is null)
       return NotFound()

     var isChanged = service.IsChanged(request, customer);

     if(!isChanged)
       return BadRequest();


     var isDuplicate = service.IsDuplicate(request);

     if(!isDuplicate)
       return BadRequest(); //500 error

     await service.Update(request)
}

Approach 2

CustomerController.cs

public Task<IActionResult> UpdateCustomer(int id, Customer request)
   {
     var customer = service.GetCustomer(id);

     if(customer is null)
       return NotFound()

     await service.Update(request, customer);
}

CustomerService.cs

public void Update(Customer request, Customer customer)
{
  if(!HasChanged(request, customer))
    throw NoChangesException();

  if(IsDuplicate(request))
   throw DuplicateException();

   db.Update(request);
}

Catch exceptions in Global exception Middleware and send the BadRequest or Internal error based on exception type.

Edit

I need to add that duplicates and no changes will be rejected by data layer. Data layer is another common OData service. I feel its expensive to call the data service for known exceptions.

Answer 1

Approach 0

Controller

public Task UpdateCustomer(Customer request)
{
     await service.Update(request)
}

Service

public void Update(Customer request)
{
   db.Update(request);
}

If there has been no change, update anyway

If the customer already exists, update it

If the customer doesn't exist, add it.

If there is a db error, throw it and convert automatically to a 500 in a global error handler