LINQ Lambda Left join with an Inner join

Question

I have written a LINQ lambda query which so far which returns all staff which do not have an associated training row which works fine. I now need to amend my where clause to use

Answer 1

Inner joins are performed with the Join method. I think your query should go something like this:

var query = db.staff
              .GroupJoin(db.training,
                         s => s.id,
                         t => t.staff_id,
                         (s, t) => new { Staff = s, Training = t.FirstOrDefault() })
              .Join(db.manager,
                    gj => gj.Staff.manager_id,
                    m => m.id,
                    (gj, m) => new { Staff = gj.Staff, Training = gj.Training, Manager = m })
              .Where(st => st.Training == null
                        && st.Manager.id == managerId);

Answer 2

You can do the following (I've not used method chaining syntax to make it more readable IMO):

var query = from s in db.staff
            join m in db.manager on s.manager_id equals m.id
            join t in db.training on s.id equals t.staff_id into tr
            from training in tr.DefaultIfEmpty()
            select new
            {
                Staff = s,
                Training = training
            };

Answer 3

Like this maybe:

var query = from s in db.staff
    join m in db.manager on s.manager_id equals m.id
    from t in db.training
        .Where(w=>w.staff_id==s.id).DefaultIfEmpty()
    select new
    {
        Staff = s,
        Training = training
    };