LINQ query (or lambda expression) to return records that match a list - linq

Question

I have a list of strings (converted from Guid) that contains the ID's of items I want to pull from my table.
Then, in my LINQ query, I am trying to figure out how to do an in clause to pull records that are in that list.
Here is the LINQ
var RegionRequests = (from r in db.course_requests
where PendingIdList.Contains(r.request_state.ToString())
select r).ToList();
It builds, but I get a run error: "System.NotSupportedException: LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression".
I would prefer to compare guid to guid, but that gets me nowhere.
Can this be converted to a lambda expression? If that is best, how?

Answer 1

LINQ to Entites tries to convert your expression to an SQL Statement. Your server didn't know the stored procedure ToString().
Fix:
var regionRequests =
from r in db.course_requests.ToList()
where PendingIdList.Contains(r.request_state.ToString())
select r;
With db.course_requests.ToList() you force LINQ to materialize your database data (if big table, you gonna have a bad time) and the ToString() is executed in the object context.

Answer 2

You stated: I have a list of strings (converted from Guid) ...
Can you NOT convert them into strings and keep it as a List< System.Guid>?? Then you can do this (assuming PendingIdGuidList is List< System.Guid>:
var regionRequets = (from r in db.course_requests
join p in PendingIdGuidList on u.request_state equals p
select r).ToList();
Edited to add:
I ran a test on this using the following code:
var db = new EntityModels.MapleCreekEntities();
List<System.Guid> PendingIdGuidList =
new List<System.Guid>() {
System.Guid.Parse("77dfd79e-2d61-40b9-ac23-36eb53dc55bc"),
System.Guid.Parse("cd409b96-de92-4fd7-8870-aa42eb5b8751")
};
var regionRequets = (from r in db.Users
join p in PendingIdGuidList on r.Test equals p
select r).ToList();
Users is a table in my database. I added a column called Test as a Uniqueidentifier data type, then modified 2 records with the following Guids.
I know it's not exactly a 1:1 of what the OP is doing, but pretty close. Here is the profiled SQL statement:
SELECT
[Extent1].[ID] AS [ID],
[Extent1].[UserLogin] AS [UserLogin],
[Extent1].[Password] AS [Password],
[Extent1].[Test] AS [Test]
FROM [dbo].[Users] AS [Extent1]
INNER JOIN (SELECT
cast('77dfd79e-2d61-40b9-ac23-36eb53dc55bc' as uniqueidentifier) AS [C1]
FROM ( SELECT 1 AS X ) AS [SingleRowTable1]
UNION ALL
SELECT
cast('cd409b96-de92-4fd7-8870-aa42eb5b8751' as uniqueidentifier) AS [C1]
FROM ( SELECT 1 AS X ) AS [SingleRowTable2]) AS [UnionAll1] ON [Extent1].[Test] = [UnionAll1].[C1]