How to return a join statement in LINQ

Question

I want to return result 3 to the main method

 var result = (from od in orders
        join em in employees on od.EmployeeID equals em.EmployeeID
        join ct in customers on od.CustomerID equals ct.CustomerID
        //orderby em.EmployeeID
        select new
        {
            od.OrderID,
            od.ShipCountry,
            ct.CompanyName,
            ct.ContactName,
            FullName = em.FirstName + ' '+ em.LastName, 
        });


 var newOrders = result.OrderBy("OrderID DESC");

 var result3 = newOrders
    .ToList()
    .Skip(rowsPerPage * (page-1))
    .Take(rowsPerPage);

 return result3;
}

 public class MyJoin {
 public int OrderID { get; set; }
 public DateTime OrderDate { get; set; }
 public string ShipCountry { get; set; }
 public string CompanyName { get; set; }
 public string ContactName { get; set; }
 public string EmployeeName { get; set; }
 }

I'm not sure how to return it as a simple

return result3;

Does not do the trick, I get an error

Cannot implicitly convert type System.Collections.Generic.List<AnonymousType#1> to System.Collections.Generic.List<UserQuery.MyJoin>

Answer 1

It is not working because in here:

select new
{
    od.OrderID,
    od.ShipCountry,
    ct.CompanyName,
    ct.ContactName,
    FullName = em.FirstName + ' '+ em.LastName, 
}

You are creating new type -> AnonymouseType, and it is not MyJoin type which you are expecting to be returned in your function. Simply use:

select new UserQuery.MyJoin
{
   OrderID = od.OrderID,
   ...
}

of course you need to fill fields from MyJoin class.

Answer 2

You cannot return an anonymous type from a function call.

You will have to explicitly define the type you expect anyhow, then

var result = (from od in orders
    join em in employees on od.EmployeeID equals em.EmployeeID
    join ct in customers on od.CustomerID equals ct.CustomerID
    //orderby em.EmployeeID
    select new UserQuery.MyJoin
    {
        od.OrderID,
        od.ShipCountry,
        ct.CompanyName,
        ct.ContactName,
        FullName = em.FirstName + ' '+ em.LastName, 
    });


var newOrders = result.OrderBy("OrderID DESC");

var result3 = newOrders
.Skip(rowsPerPage * (page-1))
.Take(rowsPerPage);
.ToList()

return result3;

Note that you do not need to materialize the result (no .ToList() needed) if this is Linq to Objects, or if the DbContext is available to the caller.

Answer 3

Specify the type -

In your case

IQueryable<UserQuery.MyJoin> result = (from od in orders
    join em in employees on od.EmployeeID equals em.EmployeeID
    join ct in customers on od.CustomerID equals ct.CustomerID
    //orderby em.EmployeeID
    select new UserQuery.MyJoin
    {
        od.OrderID,
        od.ShipCountry,
        ct.CompanyName,
        ct.ContactName,
        FullName = em.FirstName + ' '+ em.LastName, 
    });