Multiple implementations of an interface with number of Services

All ManagerService, TeamLeaderService and EngineerService are registered with the DI container. 

 The EmployeeController constructor injects IEnumerable <ISalaryService >, allowing you to iterate through all registered implementations and call their Execute methods. Alright, so you've got multiple implementations of an interface, and you want to call a specific service based on some criteria. Here’s a more detailed approach to achieve this: Define Your Interface and Implementations:

public interface ISalaryService
{
    void Execute();
}

public class ManagerService : ISalaryService
{
    public float ExecuteSalary() => 10000 + (10000 * .50) ;
}

public class TeamLeaderService : ISalaryService
{
    public float ExecuteSalary() => 10000 + (10000 * .20);
}
public class EngineerService : ISalaryService
{
    public float ExecuteSalary() => 10000 + (10000 * .10);
}

Register Multiple Implementations with Named Options: You can use named registrations in the DI container to differentiate between the services.

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddTransient <ISalaryService, ManagerService>(sp => new ManagerService());
        services.AddTransient<ISalaryService TeamLeaderService>(sp => new TeamLeaderService());
	services.AddTransient<Isalaryservice EngineerService>(sp => new EngineerService());
		
       services.AddTransient<Func<string, ISalaryService>>(serviceProvider => key =>
        {
            return key switch
            {
                "MA" => serviceProvider.GetService(),
                "TL" => serviceProvider.GetService(),
		"SE" => serviceProvider.GetService(),
                _ => throw new KeyNotFoundException()
            };
        });
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        // Configuration code
    }
}

Resolve Specific Implementation: Use a factory pattern to resolve and call the specific service based on a key.

public class EmployeeController : ControllerBase
{
    private readonly Func<string, ISalaryService> _serviceFactory;

    public EmployeeController(Func<string, ISalaryService> serviceFactory)
    {
        _serviceManager = serviceManager;
    }

    [HttpGet("ExecuteSalaryService")]
    public IActionResult ExecuteSalaryService([FromQuery] string serviceName)
    {
        var service = _serviceManager(serviceName);
        flot salary=service.ExecuteSalary();
	var data=new { totalSal=salary};
        return Ok(data);
    }
}

In this example:All ManagerService, TeamLeaderService and EngineerService are registered with the DI container.  A factory delegate (Func<string, ISalaryService >) is registered to resolve the service based on a key.  EmployeeController injects the factory and uses it to call the specific service based on the serviceName query parameter.