convert this LINQ expression into Lambda

Question

Guys, I have a hard time converting this below linq expression(left join implementation) to lambda expression (for learning).

var result = from g in groc         


        

Answer 1

Here’s how you might write this query in lambda:

var cus­tomers = new List {
new Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer1” },
new Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer2” },
};

var user­Cus­tomers = new List {
new User­Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer1”, User = “not-admin” },
new User­Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer1”, User = “admin” },
new User­Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer2”, User = “not-admin” },
new User­Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer2”, User = “admin” },
new User­Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer1”, User = “not-admin”     },
new User­Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer1”, User = “admin” },
new User­Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer2”, User = “not-admin” },
new User­Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer2”, User = “admin” }
};

Using query expres­sion

var query =
from c in cus­tomers
join uc in user­Cus­tomers on
new { c.CompanyId, c.CustomerId } equals new { uc.CompanyId, uc.CustomerId }
where c.CompanyId == “AC” && uc.User == “admin“
select c;

Using lambda expres­sions

var lambda =  cus­tomers.Where(c => c.CompanyId == “AC”) // inner sequence
.Join(userCustomers.Where(uc => uc.User == “admin”), // outer sequence
c => new { c.CompanyId, c.CustomerId }, // inner key selec­tor
uc => new { uc.CompanyId, uc.CustomerId }, // outer key selec­tor
(c, uc) => c);

Both approach yields the same result (cus­tomer with com­pany Id “AC” and cus­tomer Id “Customer1”), but as you can see, lambda expres­sion is much harder to write and read!

Hope this helps!