var query = from c in DataContextEntity
          where c.Names=="Home" and c.ParentID in
          ( from p in ParentTableName where p.Names=="Index")
          select c;

------解决方案--------------------

这叫 LAMDA表达式：

var cr = db.ControllersRoot.Where(ca => ca.Names == "Home" && ( from p in ParentTableName where p.Names=="Index").Contains(c.ParentID)).FirstOrDefault();