Entity Framework 6: Resolving user permissions by roles (IdentityUserRole) - entity-framework

Question

I have a process in which an entity changes its state, i want to get the States that current user is allowed to transfer to, i have the following expression which when evaluated i'm getting an NotSupportedException with the message:
Unable to create a constant value of type
'Microsoft.AspNet.Identity.EntityFramework.IdentityUserRole'. Only
primitive types or enumeration types are supported in this context.
var user = db.Users.Single(...); //Successfully Retrieve the user
var states = db.StateTransitions
.Join( db.RoleStateTransitions
.Join( user.Roles,
rst => rst.RoleID,
ur => ur.RoleId,
( rst, ur ) => rst ),
wst => wst.StateTransitionID,
rst => rst.StateTransitionID,
( wst, rst ) => wst.FinalState ) ;
As you can see joining with user.Roles (collection of IdentityUserRole) is the problem. What is wrong with the previous expression?

Answer 1

The problem is that user.Roles is a local collection of objects. EF has no way of translating local objects into SQL (even though they are mapped objects). But you can make it work by reducing the local collection to primitive types:
var userRoleIds = db.Users.Where(u => u.UserId == id)
.SelectMany(u => u.Roles.Select(r => r.RoleId))
.ToList();
var states = from wst in db.StateTransitions
join rst in db.RoleStateTransitions
.Where(x => userRoleIds.Contains(x.RoleId))
on wst.StateTransitionID equals rst.StateTransitionID
select wst.FinalState;
Or maybe even one query:
var states = from wst in db.StateTransitions
join rst in db.RoleStateTransitions
on wst.StateTransitionID equals rst.StateTransitionID
join role in db.Roles
on rst.ROleId equals role.RoleId
where role.Users.Any(u => u.UserId == id)
select wst.FinalState;
(Assuming there is a many to many between User and Role).