Question

I am trying to reproduce a SQL query using a LINQ to Entities query. The following SQL works fine, I just don’t see how to do it in LINQ. I have tried for a few hours today but I’m just missing something.

SELECT 
  h.ReqID,
  rs.RoutingSection
FROM ReqHeader h
JOIN ReqRoutings        rr ON rr.ReqRoutingID = (SELECT TOP 1   r1.ReqRoutingID  
                                                FROM ReqRoutings r1
                                                WHERE r1.ReqID = h.ReqID 
                                                ORDER BY r1.ReqRoutingID desc)
JOIN ReqRoutingSections rs ON rs.RoutingSectionID =  rr.RoutingSectionID  

Edit***

I was able to get this working after looking at other examples including the one provided her by Miki. Here is the code that works for me:

First I created a query called route to hold the top record I needed to join to

var route = (from rr in context.ReqRoutings
                     where rr.ReqID == id
                     orderby rr.ID descending
                     select rr).Take(1);

I was then able to join to my requisitions table and the ReqRoutings lookup table

var header = (from h in context.ReqHeaders
              join r in route on h.ID equals r.ReqID
              join rs in context.ReqRoutingSections on r.RoutingSectionID equals rs.ID
              where h.ID == id

              select {ReqID = h.ID,
                      RoutingSection = rs.RoutingSection}

Answer 1

I am using Northwnd sample database
Customers,Orders,Employees table
Here I am getting top 1 order group by customer and order’s employeeid
Please let me know If this is matching with your requirement or not

var ord = from o in NDC.Orders
          orderby o.OrderID descending
          group o by o.CustomerID into g                     
          select new {CustomerID=g.Key,Order=g.OrderByDescending(s=>s.OrderID).First() };

var res1 = from o in ord
           join emp in NDC.Employees 
           on o.Order.EmployeeID equals emp.EmployeeID into oemp
           select new {Order=o.Order,employee=oemp };

Response.Write(res1.ToList().Count);
foreach (var order in res1)
{
    Response.Write(order.Order.CustomerID + "," + 
                     order.Order.OrderID + ","+ 
                     order.Order.EmployeeID+"<br/>");
}

// Above code is working .I have tried to convert your query to linq and replace your datacontext name with ‘NDC’

var ord = from rr in NDC.ReqRoutings
          orderby rr.ReqRoutingID descending
          group rr by rr.ReqID into g
          select new 
          { 
              ReqID = g.Key, 
              ReqRoutings = g.OrderByDescending(s => s.ReqRoutingID).First() 
          };

var res1 = from o in ord
           join emp in NDC.ReqRoutingSections on o.ReqRoutings.RoutingSectionID 
             equals emp.RoutingSectionID into oemp
           select new { ReqRoutings = o.ReqRoutings, employee = oemp };

Response.Write(res1.ToList().Count);
foreach (var order in res1)
{
    Response.Write(order.ReqRoutings.ReqID + "," + 
                    order.ReqRoutings.ReqRoutingID + "," + 
                    order.ReqRoutings.RoutingSectionID + "<br/>");
}

Please let know if it is help you or not