Many-to-many insert with Entity Framework

I'm two entities in my Data Model, for example User and Role, both having the ID field as primary key. There's a many-to-many relationship between them. In the database there are three tables: Users, Roles and UsersRoles junction table.

I'm trying to add a new user to the Users table:

using(var myContext = new MyContext)
{
开发者_如何学C   var user = new User() { ... };
   user.Roles.Add(new Role() { ID = 1 });
}

The same role can be already be used by another Users, so, when I try to add a new User with the same Role, I become Primary key violation as EF tries to add a new record to the Roles table.

Is there any way to tell the Entity Framework not to add a new record to the Roles table, when such role already exists, but only update the Users and UserRoles tables? EF version 1.0

Thanks in advance.

If the role already exists in the DB you must EF tell that by attaching the role to the context:

using(var myContext = new MyContext)
{
    var role1 = new Role() { ID = 1 };
    myContext.Roles.Attach(role1);

    var user = new User() { ... };
    user.Roles.Add(role1);

    myContext.Users.AddObject(user);

    myContext.SaveChanges();
}

(I hope that this also works the same way in EF 1.)

Found a working solution, though it is not perfect:

using(var _context = new MyContext())
{
    var user = ... //User we're adding to db 
    var roles = ...//List of roles
    foreach(var role in roles)
    {
        var ro = role;
        var roleAlreadyInDB = _context.Roles.Where(r => r.ID == ro.ID).FirstOrDefault();
        if (roleAlreadyInDB != null)
            user.Roles.Add(roleAlreadyInDB);
        else user.Roles.Add(new Role() { ID = ro.ID });
    }
}

This doesn't violate Primary keys in the db.