DefaultIfEmpty Linq to Sql returning null in Moles test

Question

I made a moles in for testing my repository class and it works when I put DefaultIfEmpty(new Drivers()) but when I run the program, I get this error: Unsupported overload used for query operator 'DefaultIfEmpty'.

But when I put it back to DefaultIfEmpty(), it works fine but my*strong text* moles test now returns a null value.. Here is my code:

 var result = from p in this.context.AirPositions
                         join a in this.context.Airplane p.airplane_id equals a.id
                         join s in this.context.Status on p.status_id equals s.id
                         join dp in this.context.DriversPositions on p.id equals dp.position_id into dpJoin
                         from ds in dpJoin.DefaultIfEmpty(new DriversPosition())
                         join d in this.context.Drivers on ds.driver_id equals d.id into dsJoin
                         from drs in dsJoin.DefaultIfEmpty(new Driver())
                         orderby p.timesent descending
                         select new PositionViewModel()
                         { ... };

Answer 1

It seems there is a problem with code that runs with Linq-to-Sql and Linq-to-Object.

I solved it with the following:

var result = from p in this.context.AirPositions
             join a in this.context.Airplane on p.asset_id equals a.id
             let driver = (from dd in this.context.DriversPositions.Where(u => u.position_id == p.id)
             join d in this.context.Drivers on dd.driver_id equals d.id
             select d).FirstOrDefault()
             orderby p.timesent descending
             select new PositionViewModel() {...}

Hope this helps other people :)

Answer 2

It seems like the linq provider does not support an overload on the DefaultOrEmpty function which takes a default value.

You have to rewrite your code to something else if you want to test this with moles. I know that test should not change your code. Try to rewrite your code by using SingleOrDefault.