Few GroupJoin in one query

Question

Hi all, I'm trying to write ObjectQuery with few consistent GroupJoin, it means that there should be one main table selection + few additional LEFT JOIN. I'm doing it as following, with SelectMany method, because without it I can't access field RoleID :

var routesQuery = entities.Routes.Join(
                    entities.Locales,
                    Routes => Routes.LocaleID,
                    Locales => Locales.LocaleID,
                    (Routes, Locales) => new { Routes = Routes }
                ).GroupJoin(
                    entities.LinkRolesPermissions,
                    Routes => Routes.Routes.RouteID,
                    LinkRolesPermissions => LinkRolesPermissions.EntityID,
                    (Routes, LinkRolesPermissions) => new 
                    { 
                        LinkRolesPermissions = LinkRolesPermissions,
                        RoleID = LinkRolesPermissions.SelectMany(
                            LRS => LRS.RoleID,
                            (LRS, RoleID) => new { RoleID = LRS.RoleID }
                        )
                    }
                )
                .SelectMany(
                    LinkRolesPermissions => LinkRolesPermissions.RoleID, 
                    (LinkRolesPermissions, RoleID) => new { RoleID = RoleID }
                 ).GroupJoin(
                    entities.aspnet_Roles, 
                    LRS => LRS.RoleID, 
                    RLS => RLS.RoleId, 
                    (LRS, RLS) => new { LRS = LRS }
                );

All is working, BUT it is working as INNER JOIN in some way, i realized that SelectMany method causes this behavior. It generates this query :

SELECT  1 AS [C1],  1 AS [C2],  [Extent3].[RoleID] AS [RoleID] FROM   [dbo].[Routes] AS [Extent1] 
INNER JOIN [dbo].[Locales] AS [Extent2] ON ([Extent1].[LocaleID] = [Extent2].[LocaleID]) OR (([Extent1].[LocaleID] IS NULL) AND ([Extent2].[LocaleID] IS NULL)) 
INNER JOIN [dbo].[LinkRolesPermissions] AS [Extent3] ON ([Extent1].[RouteID] = [Extent3].[EntityID]) OR (([Extent1].[RouteID] IS NULL) AND ([Extent3].[EntityID] IS NULL))

I removed it and got the following error :

var routesQuery = entities.Routes.Join(
                    entities.Locales,
                    Routes => Routes.LocaleID,
                    Locales => Locales.LocaleID,
                    (Routes, Locales) => new { Routes = Routes }
                ).GroupJoin(
                    entities.LinkRolesPermissions,
                    Routes => Routes.Routes.RouteID,
                    LinkRolesPermissions => LinkRolesPermissions.EntityID,
                    (Routes, LinkRolesPermissions) => new 
                    { 
                        LinkRolesPermissions = LinkRolesPermissions,
                        RoleID = LinkRolesPermissions.SelectMany(
                            LRS => LRS.RoleID,
                            (LRS, RoleID) => new { RoleID = LRS.RoleID }
                        )
                    }
                )
                .GroupJoin(
                    entities.aspnet_Roles, 
                    LRS => LRS.RoleID, 
                    RLS => RLS.RoleId, 
                    (LRS, RLS) => new { LRS = LRS }
                );

The type arguments for method 'System.Linq.Enumerable.SelectMany(System.Collections.Generic.IEnumerable, System.Func>, System.Func)' cannot be inferred from the usage. Try specifying the type arguments explicitly.

Could somebody explain me this behavior, please, and advise how to fix it if possible.

Thanks in advance.

Answer 1

You're trying to eagerly load related objects. Use the Include method to do that.

http://msdn.microsoft.com/en-us/library/bb896272.aspx

IQueryable<Route> query = 
  from route in entities.Routes.Include("LinkRolesPermissions.aspnet_Roles")
  where route.Locales.Any()
  select route;

For this to work, you'll have to set up Navigation Properties.

http://msdn.microsoft.com/en-us/library/bb738520.aspx

---

PS: you don't have to project into an anonymous type each time:

(Routes, Locales) => new { Routes = Routes } 

Could be

(Routes, Locales) => Routes