LINQ InsertOnSubmit：NullReferenceException异常 [英] LINQ InsertOnSubmit: NullReferenceException

问题描述

我有这样的code：

using DC = MV6DataContext;
using MV6; // Business Logic Layer
// ...

public DC.MV6DataContext dc = new DC.MV6DataContext(ConnectionString);
IP ip = new IP(Request.UserHostAddress);
dc.IPs.InsertOnSubmit(ip);
dc.SubmitChanges();

// in Business Logic layer:
public class IP : DC.IP {
  public IP(string address) { ... }
}

在试图InsertOnSubmit（IP），我得到一个NullReferenceException（不设置到对象的实例对象引用）。 DC不是null; IP和IP的所有属性都不为null;虽然有些是空的。

Upon attempting to InsertOnSubmit(ip), I get a NullReferenceException (Object reference not set to an instance of an object). dc is not null; ip and all properties of ip are not null; though some are empty.

VS2008不会让我踏进InsertOnSubmit，所以我不知道具体是什么为空进行评估时的方式。是什么给了？

VS2008 won't let me step into InsertOnSubmit, so I have no way of knowing what specifically is null when being evaluated. What gives?

请注意：我已经检查，并通过FK关系创建的所有Linq.EntitySets是present和非空

Note: I have checked, and all Linq.EntitySets created by FK relationships are present and non-null.

推荐答案

明白了。

而不是创建从DataContext中的类继承的类，我的DC类本身扩展与业务逻辑层的部分类。从那里，我可以添加我所希望的任何构造函数和方法。

Rather than creating a class that inherits from the DataContext's class, I extend the DC class itself with a partial class in the Business Logic layer. From there I can add whatever constructors and methods I wish.

在这种情况下，这里有必要从现有（自动产生）构造复制code：

In this case, it is neccessary to copy the code from the existing (auto-generated) constructor:

public IP(string address) {
Address = address;
Domain = "";
Notes = "";
FirstAccess = DateTime.Now;
LastAccess = DateTime.Now;
this._Sessions = new EntitySet<Session>(new Action<Session>(this.attach_Sessions), new Action<Session>(this.detach_Sessions));
OnCreated(); }

不知道在这OnCreated处理程序，但它似乎是在做早去骨我的工作。现在工作得很好：）

Not sure what's in that OnCreated handler, but it seems to be doing the work that boned me earlier. Works fine now :)

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