Provider-Hosted Add-in CRUD example using CSOM

Below is a complete CRUD example of provider-hosted SharePoint Add-In using CSOM. In the controller, the CRUD is performed on a SharePoint list, "Products", which is made of [ID], [Title], [UnitPrice] and [UnitsOnStock] fields.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using Microsoft.SharePoint.Client;
using ProviderHostedCloud1Web.Models;

namespace ProviderHostedCloud1Web.Controllers
{
    [SharePointContextFilter]
    public class ProductController : Controller
    {

        // GET: Product
        public ActionResult Index()
        {
            var spContext = SharePointContextProvider.Current.GetSharePointContext(HttpContext);
            using (ClientContext cc = spContext.CreateUserClientContextForSPHost())
            {
                if (cc != null)
                {
                    List productList = cc.Web.Lists.GetByTitle("Products");
                    cc.Load(productList);
                    cc.ExecuteQuery();

                    if (productList != null)
                    {
                        CamlQuery query = CamlQuery.CreateAllItemsQuery();
                        ListItemCollection products = productList.GetItems(query);
                        cc.Load(products);
                        cc.ExecuteQuery();

                        List retVal = new List();
                        foreach (var product in products)
                        {
                            retVal.Add(new Product
                            {
                                ID = product.Id,
                                Title = product["Title"].ToString(),
                                UnitPrice = Convert.ToDecimal(product["UnitPrice"]),
                                UnitsOnStock = Convert.ToInt32(product["UnitsOnStock"])
                            });
                        }
                        return View(retVal);
                    }

                    return View();
                }
                else
                {
                    ViewBag.ErrorMessage = "Error: ClientContext is null.";
                    return View();
                }
            }

        }

        // GET: Product/Details/5
        public ActionResult Details(int id)
        {
            try
            {
                var spContext = SharePointContextProvider.Current.GetSharePointContext(HttpContext);
                using (ClientContext cc = spContext.CreateUserClientContextForSPHost())
                {
                    if (cc != null)
                    {
                        ListItem item = cc.Web.Lists.GetByTitle("Products").GetItemById(id);
                        cc.Load(item);
                        cc.ExecuteQuery();

                        if (item != null)
                        {
                            Product retVal = new Product
                            {
                                ID = item.Id,
                                Title = item["Title"].ToString(),
                                UnitPrice = item["UnitPrice"] == null ? 0.00m : Convert.ToDecimal(item["UnitPrice"]),
                                UnitsOnStock = item["UnitsOnStock"] == null ? 0 : Convert.ToInt32(item["UnitsOnStock"])
                            };

                            return View(retVal);
                        }
                        else
                        {
                            return View();
                        }
                    }
                    else
                    {
                        ViewBag.ErrorMessage = "Error: ClientContext was null. ";
                        return View();
                    }
                }
            }
            catch (Exception ex)
            {
                Exception ie = ex;
                while (ie.InnerException != null)
                {
                    ie = ie.InnerException;
                }
                ViewBag.ErrorMessage = "Error: " + ie.Message;
                return View();
            }
        }

        // GET: Product/Create
        public ActionResult Create()
        {
            return View();
        }

        // POST: Product/Create
        [HttpPost]
        public ActionResult Create(System.Web.Mvc.FormCollection collection)
        {
            string title = collection["Title"].ToString();
            decimal unitPrice = collection["UnitPrice"] == null ? 0.00m : Convert.ToDecimal(collection["UnitPrice"]);
            int unitsOnStock = collection["UnitsOnStock"] == null ? 0 : Convert.ToInt32(collection["UnitsOnStock"]);

            try
            {
                var spContext = SharePointContextProvider.Current.GetSharePointContext(HttpContext);
                using (ClientContext cc = spContext.CreateUserClientContextForSPHost())
                {
                    List productList = cc.Web.Lists.GetByTitle("Products");
                    ListItemCreationInformation creationInfo = new ListItemCreationInformation();
                    ListItem item = productList.AddItem(creationInfo);
                    item["Title"] = title;
                    item["UnitPrice"] = unitPrice;
                    item["UnitsOnStock"] = unitsOnStock;
                    item.Update();
                    cc.ExecuteQuery();

                    return RedirectToAction("Index", new { SPHostUrl = Request.QueryString["SPHostUrl"] });
                }
            }
            catch (Exception ex)
            {
                Exception ie = ex;
                while (ie.InnerException != null)
                {
                    ie = ie.InnerException;
                }
                ViewBag.ErrorMessage = "Error: " + ie.Message;
                Product product = new Product { Title = title, UnitPrice = unitPrice, UnitsOnStock = unitsOnStock };
                return View(product);
            }
        }

        // GET: Product/Edit/5
        public ActionResult Edit(int id)
        {
            var spContext = SharePointContextProvider.Current.GetSharePointContext(HttpContext);
            using (ClientContext cc = spContext.CreateUserClientContextForSPHost())
            {
                if (cc != null)
                {
                    ListItem item = cc.Web.Lists.GetByTitle("Products").GetItemById(id);
                    cc.Load(item);
                    cc.ExecuteQuery();
                    if (item != null)
                    {
                        Product product = new Product
                        {
                            ID = item.Id,
                            Title = item["Title"].ToString(),
                            UnitPrice = item["UnitPrice"] == null ? 0.00m : Convert.ToDecimal(item["UnitPrice"]),
                            UnitsOnStock = item["UnitsOnStock"] == null ? 0 : Convert.ToInt32(item["UnitsOnStock"])
                        };
                        return View(product);
                    }
                    else
                    {
                        return View();
                    }
                }
                else
                {
                    ViewBag.ErrorMessage = "Error: ClientContext was null";
                    return View();
                }

            }
        }

        // POST: Product/Edit/5
        [HttpPost]
        public ActionResult Edit(int id, System.Web.Mvc.FormCollection collection)
        {
            try
            {
                string title = collection["Title"].ToString();
                decimal unitPrice = Convert.ToDecimal(collection["UnitPrice"]);
                int unitsOnStock = Convert.ToInt32(collection["UnitsOnStock"]);

                var spContext = SharePointAcsContextProvider.Current.GetSharePointContext(HttpContext);
                using (ClientContext cc = spContext.CreateUserClientContextForSPHost())
                {
                    if (cc != null)
                    {
                        ListItem item = cc.Web.Lists.GetByTitle("Products").GetItemById(id);
                        item["Title"] = title;
                        item["UnitPrice"] = unitPrice;
                        item["UnitsOnStock"] = unitsOnStock;
                        item.Update();
                        cc.ExecuteQuery();
                        return RedirectToAction("Index", new { SPHostUrl = Request.QueryString["SPHostUrl"] });
                    }
                    else
                    {
                        ViewBag.ErrorMessage = "ClientContext was null.";
                        Product product = new Product
                        {
                            ID = id,
                            Title = title,
                            UnitPrice = unitPrice,
                            UnitsOnStock = unitsOnStock
                        };
                        return View(product);
                    }
                }
            }
            catch (Exception ex)
            {
                Exception ie = ex;
                while (ie.InnerException != null)
                {
                    ie = ie.InnerException;
                }
                ViewBag.Error = "Error: " + ie.Message;
                return View();
            }
        }

        // GET: Product/Delete/5
        public ActionResult Delete(int id)
        {
            var spContext = SharePointContextProvider.Current.GetSharePointContext(HttpContext);
            using (ClientContext cc = spContext.CreateUserClientContextForSPHost())
            {
                if (cc != null)
                {
                    ListItem item = cc.Web.Lists.GetByTitle("Products").GetItemById(id);
                    cc.Load(item);
                    cc.ExecuteQuery();

                    if (item != null)
                    {
                        Product product = new Product
                        {
                            ID = item.Id,
                            Title = item["Title"].ToString(),
                            UnitPrice = item["UnitPrice"] == null ? 0.00m : Convert.ToDecimal(item["UnitPrice"]),
                            UnitsOnStock = item["UnitsOnStock"] == null ? 0 : Convert.ToInt32(item["UnitsOnStock"])
                        };
                        return View(product);
                    }
                    else
                    {
                        return View();
                    }
                }
                else
                {
                    ViewBag.Error = "Error: ClientContext was null";
                    return View();
                }
            }

        }

        // POST: Product/Delete/5
        [HttpPost]
        public ActionResult Delete(int id, System.Web.Mvc.FormCollection collection)
        {
            string title = collection["Title"].ToString();
            decimal unitPrice = Convert.ToDecimal(collection["UnitPrice"]);
            int unitsOnStock = Convert.ToInt32(collection["UnitsOnStock"]);
            try
            {
                var spContext = SharePointContextProvider.Current.GetSharePointContext(HttpContext);
                using (ClientContext cc = spContext.CreateUserClientContextForSPHost())
                {
                    if (cc != null)
                    {
                        ListItem item = cc.Web.Lists.GetByTitle("Products").GetItemById(id);
                        item.DeleteObject();
                        cc.ExecuteQuery();
                        return RedirectToAction("Index", new { SPHostUrl = Request.QueryString["SPHostUrl"] });
                    }
                    else
                    {
                        Product product = new Product
                        {
                            ID = id,
                            Title = title,
                            UnitPrice = unitPrice,
                            UnitsOnStock = unitsOnStock
                        };
                        ViewBag.Error = "Error: ClientContext was null";
                        return View();
                    }
                }
            }
            catch (Exception ex)
            {
                Exception ie = ex;
                while (ie.InnerException != null)
                {
                    ie = ie.InnerException;
                }
                ViewBag.ErrorMessage = "Error: " + ie.Message;
                return View();
            }
        }
    }
}