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#工作.我有一个名为genesisRepository连接数据库的存储库.

我有一个表在一个名为Stream的对象中的表.它的定义如下:

[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); }
    }

}

我在我的控制器中有一个测试操作,用于在我的Stream表中创建新记录.

    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");
    }

该函数genesisRepository()如下所示:

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

我执行ActionResult时得到一个空引用错误StreamTest().genesisRepository不为null.streamTable不为null,新创建的对象stream显然也不为null.我唯一能想到的就是null是EntitySet<T>定义外来关系的属性.

所以,我将ActionResult代码修改为:

    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");
    }

但是当我尝试这个时,我收到了这个错误:

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 

我可以使用创建新记录streamTable.Context.ExecuteCommand("INSERT INTO genesis.dbo.Stream (StreamName, StreamUrl) VALUES ('Name', 'url');");.

我不明白如何从这里前进.我怎样才能简单地创建一个新记录Stream？

Answer 1

请尝试以下方法.在您的类声明中替换它:

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

有了这个:

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