ASP.NET核心-如何将自动生成的Id从用户模型插入到商家模型中

public class User
{
    public int Id { get; set; } // 自动生成的ID
    public string Name { get; set; }
    // 其他用户属性...
}

public class Merchant
{
    public int Id { get; set; } // 自动生成的ID
    public string BusinessName { get; set; }
    public int UserId { get; set; } // 外键

    // 导航属性
    public User User { get; set; }
}

public class ApplicationDbContext : DbContext
{
    public DbSet<User> Users { get; set; }
    public DbSet<Merchant> Merchants { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.Entity<Merchant>()
            .HasOne(m => m.User)
            .WithMany()
            .HasForeignKey(m => m.UserId)
            .OnDelete(DeleteBehavior.Cascade);
    }
}

public async Task<IActionResult> CreateMerchant(int userId)
{
    var user = await _context.Users.FindAsync(userId);
    if (user == null)
    {
        return NotFound();
    }

    var merchant = new Merchant
    {
        BusinessName = "New Business",
        User = user // 设置导航属性
    };

    _context.Merchants.Add(merchant);
    await _context.SaveChangesAsync();

    return RedirectToAction(nameof(Index));
}