ApiController.cs

using System.Collections.Generic;
using System.Linq;
using MyProject.Models;
using Our.Umbraco.Ditto;
using Umbraco.Web;
using Umbraco.Web.WebApi;

namespace MyProject.Controllers.WebApi
{
    public class FeaturedArticlesController : UmbracoApiController
    {
        public IEnumerable<ArticleModel> Get()
        {
            //Get Root
            var rootNode = Umbraco.TypedContentAtRoot().FirstOrDefault(node => node.DocumentTypeAlias == "Root");

            if (rootNode == null) return null;
            //Get all articles
            var articles = rootNode.Descendants().Where(
                x => x.DocumentTypeAlias.Equals("Article") &&
                x.IsVisible() && x.TemplateId > 0).ToList();

            if (!articles.Any()) return null;
            var result = articles.Select(x => x.As<ArticleModel>());
            var list = new List<ArticleModel>();
            foreach (var publishedContent in articles)
            {
                var article = publishedContent.As<ArticleModel>();
                list.Add(article);
            }
            return result;
        }
    }
}