Question

How to achieve Left Excluding JOIN using LINQ?

In SQL:

SELECT <select_list> 
FROM Table_A A
LEFT JOIN Table_B B
ON A.Key = B.Key
WHERE B.Key IS NULL

Answer 1

You need DefaultIfEmpty() for the LEFT JOIN, then you can check if the joined value is null:

var result = from a in Table_A
             join b in Table_B on a.Key equals b.Key into j
             from b in j.DefaultIfEmpty()
             where b == null
             select new { ... };