OData using $expand breaks cast operation due to wrapper

Question

I'm experiencing the same problem as addressed here:

However, the answer is not sufficient for me. First of all I cannot for the life of me find HierarchyNodeExpressionVisitor in OData 5.0.0 (not RC1) (or anywhere for that matter, tried googling around).

Second even if I did find it returning IHttpActionResult is not good enough, I need to return a typed PageResult<MyViewModel>

The stated justificiation to return IHttpActionResult is "to handle the fact that the result might not be a IQueryable<MyEntity> anymore." once the $expand operator is used.

But this doesn't make sense to me because I thought the $expand operator is used to include a navigation property on entity just like a server side Include(e => e.RelatedProperty) would. At least in my case I'm only including a property already on the Entity so I don't have to worry about it "potentially being something else".

However when using $expand=Department I cannot Cast<>() to the entity type because it cannot cast SelectAllAndExpand<MyEntity> to a MyEntity.

How can I "unwrap" the expand back to the original entity so that I can do a projection?

public PageResult<DateSnippetWithDepartmentsViewModel> GetDatesWithDepartments(ODataQueryOptions<DateSnippet> options)
{
    IQueryable query = options.ApplyTo(_context.DateSnippets, new ODataQuerySettings());;

    //Exception when using $expand.. cannot cast SelectAllAndExpand<DateSnippet> to DateSnippet
    List<DateSnippet> dateSnippets = query.Cast<DateSnippet>().ToList();

    var dateSnippetsViewModels = (from d in dateSnippets
                                    select new DateSnippetWithDepartmentsViewModel
                                    {
                                        ...
                                    });

    var result = new PageResult<DateSnippetWithDepartmentsViewModel>(
            dateSnippetsViewModels as IEnumerable<DateSnippetWithDepartmentsViewModel>,
            Request.GetNextPageLink(),
            Request.GetInlineCount());

    return result;
}

Answer 1

Try this. Hopefully should work, by the time we get to the Enumerator, the result should be a DateSnippet. What you were doing before was trying to cast in the Linq Expression tree. I suspect in the IQueryable Execute, that is resolved and converted as opposed to cast.

public PageResult<DateSnippetWithDepartmentsViewModel> GetDatesWithDepartments(ODataQueryOptions<DateSnippet> options)
{
    IQueryable query = options.ApplyTo(_context.DateSnippets, new ODataQuerySettings());;

    List<DateSnippet> dateSnippets = new List<DateSnippet>();
    foreach(DateSnippet item in query)
    {
        dateSnippets.Add(item);
    }

    var dateSnippetsViewModels = (from d in dateSnippets
                                    select new DateSnippetWithDepartmentsViewModel
                                    {
                                        ...
                                    });

    var result = new PageResult<DateSnippetWithDepartmentsViewModel>(
            dateSnippetsViewModels as IEnumerable<DateSnippetWithDepartmentsViewModel>,
            Request.GetNextPageLink(),
            Request.GetInlineCount());

    return result;
}