How to do a full outer join in Linq?

Question

I\'ve inherited a database that wasn\'t designed exactly optimally, and I need to manipulate some data. Let me give a more common analogy of the kind of thing I have to do:

Answer 1

Based on Shaul's answer, but with a little streamlining:

var q =
  from id in studentIDs
  join sc in StudentClasses on id equals sc.StudentID into jsc
  join st in StudentTeachers on id equals st.StudentID into jst
  where jst.Any() ^ jsc.Any() //exclusive OR, so one must be empty

  //this will return the group with the student's teachers, and an empty group
  //   for the student's classes - 
  //   or group of classes, and empty group of teachers
  select new { classes = jsc, teachers = jst };

  //or, if you know that the non-empty group will always have only one element:
  select new { class = jsc.DefaultIfEmpty(), teacher = jst.DefaultIfEmpty() };

Note that for a full outer join, this can work, too. Leave out the where clause and use the first select above, rather than the second.