ApplicationUser自定义对象为null Identity

Question

 public class ApplicationUser
        : IdentityUser<int, ApplicationUserLogin,
            ApplicationUserRole, ApplicationUserClaim>, IUser<int>
    {

        public int OrganisationId { get; set; }

        public string DisplayName { get; set; }

        public Organisation Organisation { get; set; }

        public UserProfile UserProfile { get; set; }
    }

和流利的api：

  modelBuilder.Entity<ApplicationUser>().Property(u => u.OrganisationId).IsRequired();
  modelBuilder.Entity<ApplicationUser>().Property(u => u.DisplayName).HasMaxLength(100);
  modelBuilder.Entity<ApplicationUser>().HasRequired(m => m.Organisation);

当我找到用户时，Organization对象始终为null：

var user = await _userManager.FindByIdAsync(1);

var organisation = user.Organisation; //this is always null.

如何通过使用流畅的api加载对象来加载或配置关系？