Getting wrong order with DropDownListFor

Question

I have the following table:

CREATE TABLE CATEGORIES
( 
   ID NUMBER(1,0) PRIMARY KEY,
   CATEGORY VARCHAR2(20)
);

INSERT INTO CATEGORIES VALUES(1,"General");
INSERT INTO CATEGORIES VALUES(2,"Interior");
INSERT INTO CATEGORIES VALUES(3,"Exterior");
INSERT INTO CATEGORIES VALUES(4,"Tuning");
INSERT INTO CATEGORIES VALUES(5,"Body");

And I have an enum that exactly matches the above table:(Please don't ask why)

public enum Category
  {General=1,Interior,Exterior,Tuning,Body}

Here's my view model:

public class OrdersViewModel{
  public IEnumerable<SelecListItem> Categories{get;set;}
  public Order Order{get;set;}
}

public Order{
   public Category Category{get;set;}
}

I use memory cache to avoid traveling to the database, so I've got the following method that gets object from cache if it exists, otherwise fetches from the database:

 public T GetItemFromCache<T>(string key, Func<T> getFromDb) where T : class
    {
        T item = MemoryCache.Default.Get(key) as T;
        if (item == null)
        {
            item = getFromDb();
            if (item != null)
                MemoryCache.Default.Add(key, item, DateTime.Now.AddMinutes(1));
        }
        return item;
    }

In my action method I do the following:

public ActionResult Index(){
 MyViewModel vm=new MyViewModel();
 vm.Categories = 
 GetItemFromCache("categories", () => 
 context.Categories.OrderBy(x => x.ID).ToList().Select(x => new 
 SelectListItem { Value = x.ID.ToString(), Text = x.Category }));
}

And finally in view I do this:

@Html.DropDownListFor(x => x.Order.Category, Model.Categories, "",)

In the action method, as you can see, I use entity framework for fetching records from database and I order items by ID. So they always have to be ordered. The problem is, periodically, the position of the last two items in the result list are swapped, so instead of being:

General,Interior,Exterior,Tuning,Body

I get

General,Interior,Exterior,Body,Tuning

And I fix this by just restarting the IIS. Recycling the pool also does the job. I don't use any javascript for populating the dropdownlist. Do you have any idea what the problem might be?

Maybe it has something to do with projecting them into SelectListItems. Try just making a List and looping through the categories and adding them to the list. — JB06, Jul 14 '15 at 12:46
I'll probably do that eventually but I'm really curious about the problem itself — Mikayil Abdullayev, Jul 14 '15 at 12:54
[Projection is not the issue](http://stackoverflow.com/questions/204505/preserving-order-with-linq). Since recycling helped, its likely something with the caching itself. My guess is the caching mechanism is causing a race condition since [I do not think your code is thread safe](http://stackoverflow.com/a/6738179/636942). — Brad C, Jul 14 '15 at 14:11
Boy, that seems to be the issue. Otherwise, there's no explanation to it. — Mikayil Abdullayev, Jul 14 '15 at 18:06

Getting wrong order with DropDownListFor

0 Answers0