Converting ListItemCollection to List<t> efficiently

Question

I am getting items from a sharepoint list, like below, and then appending these to a list of the object type. I can't help but feel this is a slow way to populate this list, looping through each list item, initialising it as its object type then adding it to the list to be returned.

        List<ObjectA> _listA = new List<ObjectA>();
        using (var ctx = spContext.CreateAppOnlyClientContextForSPHost())
        {
            if (ctx != null)
            {
                try
                {
                    CamlQuery camlQuery = new CamlQuery();
                    camlQuery.ViewXml = @"<View><Query>Query Here</Query></View>";
                    ListItemCollection configItems = ctx.Web.Lists.GetByTitle("ListName").GetItems(camlQuery);
                    ctx.Load(configItems);
                    ctx.ExecuteQuery();

                    foreach (ListItem item in configItems)
                    {
                        _listA.Add(new ObjectA(item));
                    }
                }
                catch (Exception ex)
                {
                    string strEx = ex.Message;
                }
            }
            return _listA;
        }

I have tried with the following kind of idea

List<ObjectA> _listA = configItems .Cast<ObjectA>().ToList();

But this produces the following error:

Specified method is not supported.

I feel like this could be a big overhead where I can improve the speed and performance. Any thoughts on how to improve this.

Answer 1

Here is my solution with Linq:

configItems.AsEnumerable().Select(x => ToObjectA(x)).ToList();

Answer 2

Though it is 2 years passed since the question was asked I faced the same issue.

Here's my code:

private static List<ListItem> getItems(List list, ClientContext ctx)
{
    ListItemCollection items = list.GetItems(CamlQuery.CreateAllItemsQuery());
    ctx.Load(items, icol => icol.Include(i => i.DisplayName));
    ctx.ExecuteQuery();

    var result = new List<ListItem>();
    for (int i = 0, len = items.Count; i < len; i++)
    {
        result.Add(items[i]);
    }
    return result;
}

As you can see I queried all items from the list and then return the result as a list.

At first, You should know that ToList() method from System.Core assembly implemented just like that: first some checks that collection is not null and has some elements, then calling List.Add() method for all elements in a sequence. So it wouldn't improve the perfomance if you could use ToList() method because it works almost exactly as your code.

Secondly, to proove for myself I made a collection of 1000 lists with items inside then checked my method. In case of converting items to List<ListItem> it took 203 ms in average for method to run. In case of returning raw ListItemCollection it took 202 ms.