Sorting nested collection in projection: Unable to cast object of type 'SortOp' to type 'ProjectOp'

Question

I'm using projection of query results to a custom type, which isn't a part of entity data model:

public sealed class AlgoVersionCacheItem : NotificationObject
{
    public int OrderId { get; set; }
    public string OrderTitle { get; set; }
    public int? CurrentVersion { get; set; }
    public int CachedVersion { get; set; }
    public IEnumerable<int> AvailableVersions { get; set; }
}

I want AvailableVersions to be sorted in descending order. Hence, I've tried to add sorting for AvailableVersions in projection:

        return someQueryable
            .Select(version => new AlgoVersionCacheItem
            {
                OrderId = version.OrderId,
                OrderTitle = version.Order.Title,
                CurrentVersion = version.Order.CurrentAlgoVersionId,
                CachedVersion = version.Id,
                AvailableVersions = version
                    .Order
                    .AlgoVersions
                    .Where(v => (allowUncommittedVersions || v.Statuses.Any(s => s.AlgoVersionStatusListItemId == ModelConstants.AlgoVersionCommitted_StatusId)) && v.Id != version.Id)
                    .OrderByDescending(v => v.Id) // this line will cause exception
                    .Select(v => v.Id)
            })
            .Where(item => item.AvailableVersions.Any())
            .OrderByDescending(item => item.OrderId)
            .ToArray();

With sorting, execution of the query throws an System.Data.EntityCommandCompilationException with System.InvalidCastException as inner exception:

Unable to cast object of type 'System.Data.Entity.Core.Query.InternalTrees.SortOp' to type 'System.Data.Entity.Core.Query.InternalTrees.ProjectOp'

Without .OrderByDescending(v => v.Id) everything works fine.
Is this yet another feature, that isn't supported in Entity Framework, or I've missed something?

P.S. I know, that I can sort items later at client side, but I'm wondering about sorting at the server side.

Answer 1

This is a bug in EF. I was able to repro this on both EF5 and EF6. I think you should be able to workaround the bug by filtering records before creating the results i.e.:

return someQueryable
    .Where(version => version.Order.AlgoVersions.Any(v => (allowUncommittedVersions || v.Statuses.Any(s => s.AlgoVersionStatusListItemId == ModelConstants.AlgoVersionCommitted_StatusId)) && v.Id != version.Id))
    .Select(version => new AlgoVersionCacheItem
        {
            OrderId = version.OrderId,
            OrderTitle = version.Order.Title,
                CurrentVersion = version.Order.CurrentAlgoVersionId,
                CachedVersion = version.Id,
                AvailableVersions = version
                    .Order
                    .AlgoVersions
                    .Where(v => (allowUncommittedVersions || v.Statuses.Any(s => s.AlgoVersionStatusListItemId == ModelConstants.AlgoVersionCommitted_StatusId)) && v.Id != version.Id)
                    .OrderByDescending(v => v.Id) // this line will cause exception
                    .Select(v => v.Id)
        })
    .OrderByDescending(item => item.OrderId)
    .ToArray();

I also have a feeling that this query could be simplified if you go from the other side of relationship (i.e. from Orders) but it may depend on how the someQueryable is created.