C# IEnumerable Emptied Once Accessed

Question

I'm in the midst of setting up an Umbraco 8 website and have run into some weird behaviour. The project is using .NET 4.7.2.

Basically, I have an IENumerable of type Event, a simple list of content that I'd like to render in to a list. However, whenever I do anything with the list (which has items), the list is immediately emptied. This includes simply assigning to a different variable, checking for null etc.

I don't believe this is an Umbraco 8 issue but for clarity, I'm currently running through a Surface Controller and render it by calling the following in my view:

@Html.Action("RenderUpcoming", "Events")

This is the controller:

using Index.Models.Events;
using Index.Models.PublishedContent;
using Papermoon.Umbraco.Kupo.Core.Services.Interfaces;
using System;
using System.Linq;
using System.Web.Mvc;
using Umbraco.Web.Mvc;

namespace Index.Web.Controllers.Surface
{
    public class EventsController : SurfaceController
    {
        private readonly KupoGeneralSettings _kupoGeneralSettings;

        public EventsController(IKupoSettingsService kupoSettingsService)
        {
            _kupoGeneralSettings = kupoSettingsService.GetSettings<KupoGeneralSettings>("kupoGeneralSettings");
        }

        public ActionResult RenderUpcoming()
        {
            UpcomingEventsModel model = new UpcomingEventsModel();

            model.Title = "Upcoming Events";

            model.Events = Umbraco.ContentAtXPath("root/homepage/events/event").Select(x => new Event(x));

            model.Events = model.Events.Where(x => x.StartDate > DateTime.Now).OrderBy(x => x.StartDate).Take(3);

            model.TotalEvents = model.Events.Count();

            model.EventListingLink = _kupoGeneralSettings.EventListingLink;

            return PartialView("~/Views/Partials/Events/UpcomingEvents.cshtml", model);
        }
    }
}

So here, when I call model.Events = model.Events.Where(x => x.StartDate > DateTime.Now).OrderBy(x => x.StartDate).Take(3); - I have results then when I do model.TotalEvents = model.Events.Count(); the list (model.Events) is then empty.

This also happens when I assign to another variable, when I call model.Events.Any(), or when I even do Model.Events != null.

It's potentially easier to show this than tell so see the accompanying gif of this happening: https://i.sstatic.net/cEC77.gif

Thanks,

Ben

Answer 1

Sure – you don't know the actual type of the object other than that it's something you can iterate over (an IEnumerable).

It could be a generator that returns an infinite stream of things, for instance (well, in this case you know it's not).

If you need a concrete collection, you could use .ToList() to cast it into a List<> you can certainly iterate over multiple times.