您好，

所有类都需要公开主键属性，因此您需要添加一个Profile.UserId属性。完成后，您可以按如下方式映射关系：

All classes need to expose a primary key property, so you would need to add a Profile.UserId property. Once you have done that you can map the relationship as follows:

public class ProfileContext : DbContext
{
  public DbSet<User> Users { get; set; }
  public DbSet<Profile> Profiles { get; set; }

  protected override void OnModelCreating(ModelBuilder modelBuilder)
  {
    modelBuilder.Entity<Profile>()
      .HasKey(p => p.UserId);

    modelBuilder.Entity<User>()
      .HasOptional(u => u.Profile)
      .WithRequired()
      .HasConstraint((u, p) => u.UserId == p.UserId);
  }
}

public class User
{
  public int UserId { get; set; }
  public string Username { get; set; }
  public Profile Profile { get; set; }
}

public class Profile
{
  public int UserId { get; set; }
  public string FirstName { get; set; }
  public string LastName { get; set; }
  public string PostalCode { get; set; }
}