Controller class pattern

Question

The GetDropdownList() function is being called on a couple of controllers based on this example and it may be called in many other controllers, so this code is being repeated. I was thinking of encapsulating this portion of code to the base class and call that base class in these controllers, but I got stuck and don't know how to implement it. Can you please show me a way using SOLID principles?

public interface IDropdownListEntity
{
    string Value { get; set; }
    string Text { get; set; }
}

public sealed class DropdownListEntity: IDropdownListEntity
{
    public string Value { get; set; }
    public string Text { get; set; }
}

public class CountryController : ApiController
{
    //Returns the list of countries
    public IEnumerable<IDropdownListEntity> GetDropdownList()
    {
        CountryStore store = new CountryStore();

        return store.SimpleSortedListByName<DropdownListEntity>();
    }
}

public class CityController : ApiController
{
    //Returns the list of cities
    public IEnumerable<IDropdownListEntity> SortedListForDropdown()
    {
        CityStore store = new CityStore();

        return store.SimpleSortedListByName<DropdownListEntity>();
    }
}

Answer 1

1. Web API should not be bound to a particular UI

   API calls should not bound to a user interface requirement, so that it could be used in multiple places without any addition requirement. In the above code, it is returning a list of dropdownlist values rather than a list of entities.

   Your controller code may look like this:

   public class ConstantsController : ApiController
   {
       private readonly IConstantRepository _constantRepository;
   
       public ConstantsController(IConstantRepository constantRepository)
       {
           _constantRepository = constantRepository;
       }
   
   
       [Route("Constants/City")]
       [HttpGet]
       public IEnumerable<City> GetCity()
       {
           return _constantRepository.GetCity();
       }
   
   
       [Route("Constants/Country")]
       [HttpGet]
       public IEnumerable<Country> Country()
       {
           return _constantRepository.GetCountry();
       }
   }
   

   Note: I am using Web API 2 for this code.

   This code can be used by any kind of application like this:

   http://yoururl/Constants/Country

2. Use a DI container to inject dependencies into your controller

   Use Unity or a simple injector to inject dependencies. It will help you to isolate components.

   public interface IConstantRepository
   {
       IEnumerable<City> GetCity();
   
       IEnumerable<Country> GetCountry();
   }
   

Also, include unit tests in your applications.