当对象有关系时，使用LINQ to SQL来添加记录是否有秘密？

Question

我在LINQ to SQL，ASP.NET MVC和C＃中工作。我有一个名为genesisRepository的存储库连接到数据库。

我在一个名为Stream的对象中有一个表。它的定义是这样的：

[Table] 
public class Stream 
{ 
    [HiddenInput(DisplayValue = false)] 
    [Column(IsPrimaryKey = true, IsDbGenerated = true, AutoSync = AutoSync.OnInsert)] 
    public long StreamID { get; set; } 

    [Required(ErrorMessage = "Please enter a stream name")] 
    [Column] 
    public string StreamName { get; set; } 

    /* Other columns removed for brevity */ 

    [Required(ErrorMessage = "Please enter a stream URL")] 
    [Column] 
    public string StreamUrl { get; set; } 

    private EntitySet<StreamEntry> _StreamEntry; 
    [System.Data.Linq.Mapping.Association(Storage = "_StreamEntry", OtherKey = "StreamID")] 
    public EntitySet<StreamEntry> StreamEntry 
    { 
     get { return this._StreamEntry; } 
     set { this._StreamEntry.Assign(value); } 
    } 

    private EntitySet<Stream2FieldTypes> _Stream2FieldTypes; 
    [System.Data.Linq.Mapping.Association(Storage = "_Stream2FieldTypes", OtherKey = "StreamID")] 
    public EntitySet<Stream2FieldTypes> Stream2FieldTypes 
    { 
     get { return this._Stream2FieldTypes; } 
     set { this._Stream2FieldTypes.Assign(value); } 
    } 

} 

我有我的Stream表中创建新记录在我的控制器的测试动作。

public ActionResult StreamTest() 
    { 
     // create new stream 
     var stream = new Genesis.Domain.Entities.Stream(); 

     stream.StreamUrl = "url"; 
     stream.StreamName = "name"; 
     stream.StreamBody = null; 
     stream.StreamTitle = null; 
     stream.StreamKeywords = null; 
     stream.StreamDescription = null; 

     genesisRepository.CreateStream(stream); 

     return View("Index"); 
    } 

功能genesisRepository()看起来是这样的：

public long CreateStream(Stream stream) 
    {    
     streamTable.InsertOnSubmit(stream); 
     streamTable.Context.SubmitChanges(); 
     return stream.StreamID; 
    } 

我得到一个空引用错误，当我执行的ActionResult StreamTest()。 genesisRepository不为空。 streamTable不为空，并且新创建的对象stream也显然不为空。我能想到的唯一的东西是空的EntitySet<T>属性定义的外国关系。

所以，我修改了代码的ActionResult是这样的：

public ActionResult StreamTest() 
    { 
     // create new stream 
     var stream = new Genesis.Domain.Entities.Stream(); 

     stream.Stream2FieldTypes = new EntitySet<Stream2FieldTypes>(); // new 
     stream.StreamEntry = new EntitySet<StreamEntry>(); // new 
     stream.StreamUrl = "url"; 
     stream.StreamName = "name"; 
     stream.StreamBody = null; 
     stream.StreamTitle = null; 
     stream.StreamKeywords = null; 
     stream.StreamDescription = null; 

     genesisRepository.CreateStream(stream); // CreateStream() returns ID as long 

     return View("Index"); 
    } 

但是，当我尝试了，我得到这个错误：

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object. 
Source Error: 
Line 58:   { 
Line 59:    get { return this._Stream2FieldTypes; } 
Line 60:    set { this._Stream2FieldTypes.Assign(value); } <-- the offending line 
Line 61:   } 
Line 62: 
Source File: C:\path\to\Stream.cs Line: 60 

我可以创建一个使用streamTable.Context.ExecuteCommand("INSERT INTO genesis.dbo.Stream (StreamName, StreamUrl) VALUES ('Name', 'url');");的新纪录。

我不明白如何从这里前进。我如何简单地创建Stream的新纪录？

Answer 1

请尝试以下操作。在你的类声明替换此：

public class Stream 
{ 
    private EntitySet<StreamEntry> _StreamEntry; 
    private EntitySet<Stream2FieldTypes> _Stream2FieldTypes; 
} 

与此：

public class Stream 
{ 
    private EntitySet<StreamEntry> _StreamEntry = new EntitySet<StreamEntry>(); 
    private EntitySet<Stream2FieldTypes> _Stream2FieldTypes = new EntitySet<Stream2FieldTypes>(); 
}