.net c#如何公开联接表?

I'm trying to follow this idea from Jimmy Bogard on avoiding Many-to-Many-Mappings in ORMs

Given this setup I want to be able to also directly expose the 'Join' object in the relationship.

Objects

• User
• Role
• UserRole (association object)

Code:

public class User
{
    public Guid Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Role> Roles { get; set; }
}

public class Role
{
    public Guid Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<User> Users { get; set; }
}

public class UserRole
{
    public Guid UserId { get; set; }
    public Guid RoleId { get; set; }
    public User User { get; set; }
    public Role Role { get; set; }
}

public class MyContext : DbContext 
{

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        //modelBuilder.Entity<UserRole>().HasKey(u => new { u.RoleId, u.UserId });
        modelBuilder.Entity<User>().HasMany(x => x.Roles).WithMany(x => x.Users).Map(m =>
        {
            m.ToTable("UserRoles");
            m.MapLeftKey("UserId");
            m.MapRightKey("RoleId");
        });
    }

    public DbSet<User> Users { get; set; }
    public DbSet<Role> Roles { get; set; }
    //public DbSet<UserRole> UserRoles { get; set; } 
}

If I add a migration for this I get what I expect.

public override void Up()
{
    CreateTable(
        "dbo.Roles",
        c => new
            {
                Id = c.Guid(nullable: false),
                Name = c.String(),
            })
        .PrimaryKey(t => t.Id);

    CreateTable(
        "dbo.Users",
        c => new
            {
                Id = c.Guid(nullable: false),
                Name = c.String(),
            })
        .PrimaryKey(t => t.Id);

    CreateTable(
        "dbo.UserRoles",
        c => new
            {
                UserId = c.Guid(nullable: false),
                RoleId = c.Guid(nullable: false),
            })
        .PrimaryKey(t => new { t.UserId, t.RoleId })
        .ForeignKey("dbo.Users", t => t.UserId, cascadeDelete: true)
        .ForeignKey("dbo.Roles", t => t.RoleId, cascadeDelete: true)
        .Index(t => t.UserId)
        .Index(t => t.RoleId);
}

As soon as I add a DBset to the DbContext for the UserRoles object. EF can't find the PK for the UserRoles object.

UserRoles: EntityType: EntitySet 'UserRoles' is based on type 'UserRole' that has no keys defined.

I then try specifying the Key like this:

modelBuilder.Entity<UserRole>().HasKey(u => new { u.RoleId, u.UserId });

But EF doesn't know I want to use the same UserRoles table because it add's a 2nd table for that object.

CreateTable(
"dbo.UserRoles1",
c => new
    {
        RoleId = c.Guid(nullable: false),
        UserId = c.Guid(nullable: false),
    })
.PrimaryKey(t => new { t.RoleId, t.UserId })
.ForeignKey("dbo.Roles", t => t.RoleId, cascadeDelete: true)
.ForeignKey("dbo.Users", t => t.UserId, cascadeDelete: true)
.Index(t => t.RoleId)
.Index(t => t.UserId);

How can I instruct the DbModelBuilder that I want to only use a single UserRole table?

I have a demo .sln for this problem on github