entity code first many-to-many relations saving - ef-code-first

Question

I have spent a day with this problem. There are these entitites:
public class UserRole
{
[Key]
public virtual int Id { get; set; }
public virtual string Name { get; set; }
public virtual ICollection<Privilege> Privileges { get; set; }
}
public class Privilege
{
[Key]
public virtual int Id { get; set; }
public virtual string Name { get; set; }
public virtual ICollection<UserRole> Roles { get; set; }
}
And this configuration in context:
modelBuilder.Entity<UserRole>().HasMany<Privilege>(a => a.Privileges).WithMany(a => a.Roles)
.Map(m =>
{
m.MapLeftKey("RoleId");
m.MapRightKey("PrivilegeId");
m.ToTable("RolesPrivilegesMapping");
});
And this test code:
UserRole role;
//get role entity from context
//write privileges count
using (VaultContext context = new VaultContext(connectionString))
{
role = context.UserRoles.Where(a => a.Name == "Users").FirstOrDefault();
Console.WriteLine(role.Privileges.Count.ToString()); //writes 0
}
//make offline changes
//the privilege already exists in database
role.Privileges.Add(new Privilege() { Id = 1, Name = "Login" });
//save changes to database
using (VaultContext context = new VaultContext(connectionString))
{
List<Privilege> privileges = new List<Privilege>();
foreach (Privilege p in role.Privileges)
{ privileges.Add(p); }
foreach (Privilege p in privileges)
{ context.Privileges.Attach(p); }
role.Privileges.Clear();
context.UserRoles.Attach(role);
context.Entry(role).State = System.Data.EntityState.Modified;
foreach (Privilege p in privileges)
{ role.Privileges.Add(context.Privileges.Find(p.Id)); }
context.SaveChanges();
}
//reload the role entity
//write privileges count
using (VaultContext context = new VaultContext(connectionString))
{
Console.WriteLine(context.UserRoles.Where(a => a.Name == "Users").FirstOrDefault().Privileges.Count.ToString()); //writes 0
}
The Users role and Login privilege is already in database. So I try to add privilege Login to Users role.
But relations are not saved in database - the RolesPrivilegesMapping table doesn't contain record with id corresponding with Users role and Login privilege.
If I simply add directly - it works, but it is not my target:
new UserRole()
{
Name = "Administrators",
Privileges = new List<Privilege>()
{
new Privilege() { Name = "Login" }
}
}
Could anyone advice me how to add only many-to-many relations if all entities exist in database?
I'm using EF 5.0. I have tried it with EF 4.3 with same result.

Answer 1

If all your wanting to do is attach existing entries in your database, could you do somethign a bit simpler?
using( VaultContext context = new VaultContext( ) )
{
role = context.UserRoles.FirstOrDefault(a => a.Name == "Users");
Privilege p = context.Privileges.FirstOrDefault(pr => pr.Name == "Login");
role.Privileges.Add(p);
context.SaveChanges();
}

Answer 2

Thank you.
This is my solution: (role is changed offline)
UserRole dbRole = context.UserRoles.Find(role.Id);
dbRole.Privileges.Clear();
foreach (Privilege p in role.Privileges)
{
dbRole.Privileges.Add(context.Privileges.Find(p.Id));
}
context.Entry(dbRole).State = System.Data.EntityState.Modified;