Question

I have a pretty standard model for Users and Roles:

+-------+   +-----------+   +-------+
| Users |   | UserRoles |   | Roles |
+-------+   +-----------+   +-------+
| ID (P)| < | UserID (P)|   | ID (P)|
| ...   |   | RoleID (P)| > | ...   |
+-------+   +-----------+   +-------+

I am using the Entitiy framework as my ORM and I am trying to construct – in a single Linq query – my ViewModel, definied below:

public class RoleDetail {
  public class RoleUser {
    public int ID { get; set; }
    public string Username { get; set; }
  }
  public int ID { get; set; }
  public string Rolename { get; set; }
  public bool Active { get; set; }
  public IEnumerable<RoleUser> Users { get; set; }
}

I figured that the following query should work:

var query = Context.Roles
                   .Include("Users")
                   .Where(r => r.ID == id)
                   .Select(r => new RoleDetail() {
                      ID = r.ID,
                      Rolename = r.Rolename,
                      Active = r.Active,
                      Users = r.Users
                               .Select(u => new RoleDetail.RoleUser() {
                                  ID = u.ID,
                                  Username = u.Username
                                })
                                .ToList()
                    })
                   .FirstOrDefault();

However, this throws the following error:

LINQ to Entities does not recognize the method
‘System.Collections.Generic.List [RolesRepository+RoleDetail+RoleUser]
ToList[RoleUser]
(System.Collections.Generic.IEnumerable[RolesRepository+RoleDetail+RoleUser])’
method, and this method cannot be translated into a store expression.

I haven’t worked with Linq a lot, so I am quite sure that my query is wrong somehow. Can someone show me where my query is going wrong and if there is a better way to accompish what I’m trying to achieve?

Thank you in advance!

Answer 1

Little experience with linq-to-entities, so this is a shot in the dark:

Why do you need .ToList()?

.Select() already returns an IEnumerable, so it should work without.

ToList() returns a List, not an IList or similar interface, but a concrete c# class. So I’d imagine that Linq to Entities cannot translate that into its own behind the scenes syntax

Does this work?

       var query = Context.Roles
               .Include("Users")
               .Where(r => r.ID == id)
               .Select(r => new RoleDetail() {
                  ID = r.ID,
                  Rolename = r.Rolename,
                  Active = r.Active,
                  Users = r.Users
                           .Select(u => new RoleDetail.RoleUser() {
                              ID = u.ID,
                              Username = u.Username
                            })
                            // .ToList()
                })
               .FirstOrDefault();