Updating entity framework entity with many to many relationship - entity-framework

Question

I have (2) entities, they are as follows:
[Table("User")]
public class User
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int UserId { get; set; }
[Required]
[MaxLength(20)]
public string Name { get; set; }
public ICollection<Role> Roles { get; set; }
public User()
{
this.Roles = new Collection<Role>();
}
}
[Table("User")]
public class Role
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int RoleId{ get; set; }
[Required]
[MaxLength(20)]
public string Name { get; set; }
public ICollection<User> Users { get; set; }
public Role()
{
this.Users = new Collection<User>();
}
}
This creates three tables in my database, User, Role and UserRole.
I am leveraging a generic repository, my Add and Update look like the following:
public virtual void Add(TEntity entity)
{
_dbSet.Add(entity);
}
public virtual void Update(TEntity entity)
{
_dbSet.Attach(entity);
_dbContext.Entry(entity).State = EntityState.Modified;
}
If I want to add a new User with Roles, I have to do the following in my UserRepository, which inherits from my generic repository.
public override void Add(User entity)
{
foreach (var role in entity.Roles)
_dbContext.Roles.Attach(role);
base.Add(entity);
}
This seems clunky, but it works.
My trouble is now when I want to update a User, say add a new Role. I thought I could do something similar.
public override void Update(User entity)
{
foreach (var role in entity.Roles)
_dbContext.Roles.Attach(role);
base.Update(entity);
}
But this does not work ... any ideas on what I am doing wrong would be appreciated!
Update
My use case is I have an existing User with X Roles, I add Y number of Roles, I want to update the User with the Y number of new Roles.

Answer 1

You shouldn't need to do that. If the role does not yet exist, you would do something like this:
var user = new User { Name="Fred" }
user.Roles.Add(new Role { Name="Accounting" });
context.Add(user);
If you are adding an existing role, then you need to get that role first
var role = context.Roles.Single(x => x.Name="Accounting");
var user = new User { Name="Fred" }
user.Roles.Add(role);
context.Add(user);