DbContextModels.cs

public class RoleResourceActivity {
    public Int32 ResourceId { get; set; }
    public virtual Resource Resource { get; set; }
    public Int32 ActivityId { get; set; }
    public virtual Activity Activity { get; set; }        
    public Int32 RoleId { get; set; }
    public Role Role { get; set; }
}

// User-Role relationship cardinality is many to many:

public class User {
    public Int32 Id { get; set; }
    public virtual ISet<Role> Roles { get; set; }
    // ctors are omitted
}

public class Role {
    public Int32 Id { get; set; }
    public String Name { get; set; }
    public virtual ISet<User> Users { get; set; }
    public virtual ISet<RoleResourceActivity> RoleResourceActivities { get; set; }
    // ctors are omitted
}

public class Activity {
    public Int32 Id { get; set; }
    public String Name { get; set; }
    public virtual ISet<RoleResourceActivity> RoleResourceActivities { get; set; }

    public Activity(String name) : this() {
        this.Name = name;
    }

    protected Activity() {
	this.RoleResourceActivities = new HashSet<RoleResourceActivity>();
    }
}

public class Resource {
    public Int32 Id { get; set; }
    public String Name { get; set; }
    public virtual ISet<RoleResourceActivity> RoleResourceActivities { get; set; }

    public Resource(String name) : this() {
        this.Name = name;
    }

    protected Resource() {
        this.RoleResourceActivities = new HashSet<RoleResourceActivity>();
    }
}

public class AppDbContext : DbContext {
    public DbSet<User> Users { get; set; }
    public DbSet<RoleResourceActivity> RoleResourceActivities { get; set; }
    public DbSet<Activity> Activities { get; set; }
    public DbSet<Resource> Resources { get; set; }
    public DbSet<Role> Roles { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder) {
        modelBuilder.Entity<Activity>().HasKey(i => i.Id);
        modelBuilder.Entity<Resource>().HasKey(i => i.Id);
        modelBuilder.Entity<User>().HasKey(i => i.Id);
        modelBuilder.Entity<RoleResourceActivity>().HasKey(i => new {i.ResourceId, i.ActivityId, i.RoleId});

        base.OnModelCreating(modelBuilder);
    }

    public AppDbContext() : base("AppDb") { 
        Database.SetInitializer<AppDbContext>(new AppDbContextInitializer());
    }
}