实体框架CTP4建模和映射问题/问题

Question

我有一个网站，允许用户在主站点中创建尽可能多的微站点。用户也可以将其他用户设置为其微站点的管理员，用户可以关注其他微站点。我不知道我做错了，（这似乎与CTP3工作），但是当我尝试做简单的东西一样

var site = _siteRepo.SingleOrDetault(x => x.Id == id); 

site.Moderators.Add(user1); 

我得到一个System.NullReferenceException：未设置为一个对象的实例对象引用。

这是我的实体的样子，以及我如何映射它们。

public class User : IEntity 
    { 
     private DateTime _createdAt; 
     private DateTime _lastActivityAt; 
     public User() 
     { 
      _createdAt = SystemTime.Now(); 
      _lastActivityAt = SystemTime.Now(); 
     } 

     public virtual long Id { get; private set; } 
     public virtual string Email { get; set; } 
     public virtual string Name { get; set; } 
     public virtual string PasswordHash { get; set; } 
     public virtual string PasswordSalt { get; set; } 
     public virtual bool IsConfirmed { get; set; } 
     public virtual ICollection<Site> Moderator { get; set; } 
     public virtual ICollection<Site> Following { get; set; } 
     public virtual ICollection<Site> Sites { get; set; } 
     public virtual DateTime LastActivityAt 
     { 
      [DebuggerStepThrough] 
      get { return _lastActivityAt; } 
      [DebuggerStepThrough] 
      set { _lastActivityAt = value; } 
     } 
     public virtual DateTime CreatedAt 
     { 
      [DebuggerStepThrough] 
      get { return _createdAt; } 
      [DebuggerStepThrough] 
      set { _createdAt = value; } 
     } 

     public Role Role 
     { 
      get { return (Role) InternalRole; } 
      set { InternalRole = (int) value; } 
     } 
     [EditorBrowsable(EditorBrowsableState.Never)] 
     public virtual int InternalRole 
     { 
      [EditorBrowsable(EditorBrowsableState.Never)] 
      get; 
      [EditorBrowsable(EditorBrowsableState.Never)] 
      set; 
     } 
    } 

public class Site : IEntity 
    { 
     private DateTime _createdAt; 

     public Site() 
     { 
      _createdAt = SystemTime.Now(); 
     } 
     public virtual long Id { get; set; } 
     public virtual string Slug { get; set; } 
     public virtual bool IsPrivate { get; set; } 
     public virtual bool IsActive { get; set; } 
     public virtual bool IsAdminRestricted { get; set; } 
     public virtual bool HasDonationPage { get; set; } 
     public virtual SiteData SiteData { get; set; } 
     public virtual Theme Theme { get; set; } 
     public virtual User User { get; set; } 
     public virtual ICollection<User> Moderators { get; set; } 
     public virtual ICollection<User> Following { get; set; } 
     public virtual ICollection<SiteAnnouncement> SiteAnnouncements { get; set; } 
     public virtual ICollection<SiteLink> SiteLinks { get; set; } 
     public virtual ICollection<SitePost> SitePosts { get; set; } 
     public virtual SiteDonation SiteDonation { get; set; } 
     public virtual DateTime CreatedAt 
     { 
      get { return _createdAt; } 
      set { _createdAt = value; } 
     } 

    } 


     public UserMap() 
     { 
      HasKey(u => u.Id); 
      Property(u => u.Id).IsIdentity(); 
      Property(u => u.Name).IsRequired().IsVariableLength().HasMaxLength(75); 
      Property(u => u.Email).IsRequired().IsVariableLength().HasMaxLength(75); 
      Property(u => u.PasswordHash).IsRequired().IsVariableLength().HasMaxLength(215); 
      Property(u => u.PasswordSalt).IsRequired().IsVariableLength().HasMaxLength(88); 
      Property(u => u.IsConfirmed); 
      Property(u => u.LastActivityAt); 
      Property(u => u.CreatedAt); 
      Property(u => u.InternalRole); 
      MapSingleType(u => new 
            { 
             u.Id, 
             u.Name, 
             u.Email, 
             u.PasswordHash, 
             u.PasswordSalt, 
             u.IsConfirmed, 
             Role = u.InternalRole, 
             u.LastActivityAt, 
             u.CreatedAt 
            }).ToTable("User"); 
     } 

     public SiteMap() 
     { 
      HasKey(s => s.Id); 
      Property(s => s.Id).IsIdentity(); 
      Property(s => s.HasDonationPage); 
      Property(s => s.IsActive); 
      Property(s => s.IsAdminRestricted); 
      Property(s => s.IsPrivate); 
      Property(s => s.Slug).IsRequired().IsVariableLength().HasMaxLength(125); 
      Property(s => s.CreatedAt); 
      MapSingleType(s => new 
            { 
             s.Id, 
             ThemeId = s.Theme.Id, 
             UserID = s.User.Id, 
             s.HasDonationPage, 
             s.IsActive, 
             s.IsAdminRestricted, 
             s.IsPrivate, 
             s.Slug, 
             s.CreatedAt 
            }).ToTable("Sites"); 
     } 

Answer 1

在向其添加对象之前，需要对ICollection的空属性进行检查。

或设置构造默认：

public User() 
     { 
      _createdAt = SystemTime.Now(); 
      _lastActivityAt = SystemTime.Now(); 
      Moderator = new List<Site>(); 
      Following = new List<Site>(); 
      Sites = new List<Site>(); 
     }