views:

1566

answers:

5

I have this 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) { ... }
}

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

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

+1  A: 

You can try to see what's happening, what changes will be done, if you place a breakpoint just before SubmitChanges, and do a quick watch of dc.GetChangeSet().

CMS
OK; it never gets to that line because the exception is thrown on InsertOnSubmit.
tsilb
That wasn't the solution, but +1 for providing something useful I hadn't known.
tsilb
+1  A: 

Is this a designer generated DataContext or your own hand-built one. I suspicious that the IPs table may not be instantiated at the time you try your InsertOnSubmit(). I can't see how this would happen with a designer-generated DataContext, but I've been known to forget to initialize my collections from time to time in my own code.

tvanfosson
tsilb
That wasn't the solution, but +1 as it steered me in the general direction that provided the solution.
tsilb
+3  A: 

Got it.

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.

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(); }

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

tsilb
thx :D LINQ boned me the same way ;)
SpoBo
I think that calling the auto-genrated constructor (using :this()) is better than copy-pasting it.
svick
+3  A: 

Hey tsilb,

Since the default constructor already initializes base(), this._Sessions and runs the OnCreated method, all you need to do in your extended constructor is this:

public IP(string address) : this()
{
    Address = address;
    Domain = "";
    Notes = "";
    FirstAccess = DateTime.Now;
    LastAccess = DateTime.Now;
}
Ah, Touché.
tsilb
+5  A: 

Actually it's better to add a call to your constructor that also calls the generic constructor such as:

public IP(string address) : this() { ... }

Max