How to cast SelectExpandQueryOption to IQueryable<T> when using OData in WebAPI?

Question

I have a WebAPI that is written in C# on the top of ASP.NET Core/5 framework.

I enabled odata for my API. I am trying to manually apply the odata filter, order by clause, select columns and the expands.

Here is how I am trying to manually build the query using the ODataQueryOptions

protected IQueryable<TModel> BuildQuery(ODataQueryOptions<TModel> queryOptions, ODataQuerySettings settings)
{
    IQueryable<TModel> query = DbSet;

    if (queryOptions.SelectExpand != null)
    {
        var queryable = queryOptions.SelectExpand.ApplyTo(query, settings);

        query = queryable.Cast<TModel>(); // this causes an error
    }

    if (queryOptions.Filter != null)
    {
        query = queryOptions.Filter.ApplyTo(query, settings) as IQueryable<TModel>;  // this works!
    }

    if (queryOptions.OrderBy != null)
    {
        query = queryOptions.OrderBy.ApplyTo(query); // this works!
    }

    return query;
}

Everything above works great up until I try to expand a navigation property. When I do I get the following error

System.InvalidOperationException: 'No coercion operator is defined between types 'Microsoft.AspNetCore.OData.Query.Wrapper.SelectAllAndExpand`1[MyModel]' and 'MyModel'.'

Is there some sort of mapping that I need to do when defining the IEdmModel to build the navigation relations?

How can I correctly convert/cast IQueryable<Microsoft.AspNetCore.OData.Query.Wrapper.SelectAllAndExpand<TEntity>> to IQueryable<TEntity>?

Here is the code behind SelectAllAndExpand

Answer 1

You can't directly cast

var queryable = queryOptions.SelectExpand.ApplyTo(query, settings);

to IQueryable<TModel>, because it different type of object.

If there is no Projection (Select) or Expand - you will get a regular object, but after Projection and Expand - it's a completely different thing. Depending on your tasks, you should handle SelectAllAndExpand<TModel> or remove SelectExpand.ApplyTo(..).