Taken from Is there a way to find a table in a DBML file in Visual Studio 2008? – Stack Overflow.

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One solution is to simply delete the old users and re-create, but this can be a real pain in the neck, especially if you have complex rights or can’t delete them because of the way things are configured. You can get around this with renaming users and re-creating and then switching things over and deleting the old ones, but this is all very tedious.

Fortunately, there is a stored procedure that will deal with the problem. First of all, create the new login without mapping it to a user. Once you have done that, open a query window in the appropriate database and run

sp_change_users_login ‘auto_fix’, ‘username‘

where username is the username that you want to fix.  It takes a split second to run, so you can do a whole load of them without too much hassle.

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The first one is the NullReferenceException, which usually comes with the message “Object reference not set to an instance of an object.”. This Exception occurs when you try to access an object reference which is set to Nothing.

First of all, you need to understand the difference between value types and reference types in .NET. With a value type, we only care about what data is stored within it. With a reference type, the actual instance of the type is important in itself. For example, we may have an Integer, which contains 10. Integers are value types, and there is generally nothing particularly different between one number 10 and another number 10 if they are both Integers, so they are effectively identical.

Reference types on the other hand are different. If we have two customers, and both of them happen to be called “John Smith”, we don’t want to treat them as being the same thing just because they have the same name. The other difference with reference types is that we can have an empty reference – Nothing (or null in c#).

In fact, behind the scenes, reference types store a location in memory of the instance. In older programming languages, such as C/C++, these were known as pointers, and you could actually access them just like a number and change the item that they were pointing to with arithmetic operators (+/-/increment/decrement etc.) This created a number of potential problems and so references were created to protect pointers from causing too much damage. References also the garbage collector to keep track of what is referencing an object instance so that the instance can be cleared up when it is no longer in use.

The NullReferenceException is thrown when you attempt to access an object reference which is set to Nothing. This can easily happen because as mentioned above, all variables of a reference type will be initialised to Nothing by the .NET framework if they have not been explicity set to something else.

For example,

        Dim c As Customer
        c.Name = "John Smith"

The second line in the above piece of code will throw a NullReferenceException as the variable c is still set to Nothing, and when the .NET framework attempts to access the Name field, it will find that the object does not exist.

This is easily resolved by setting c to whatever Customer you wish to use, or to a New Customer.

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I was using Microsoft SQL Management Studio 2008. When I attempted to pop out the list of databases on a server in object explorer, I got the following error: -

“Unable to cast COM object of type ‘System.__ComObject’ to interface type ‘Microsoft.VisualStudio.OLE.Interop.IServiceProvider’. This operation failed because the QueryInterface call on the COM component for the interface with IID ‘{6D5140C1-7436-11CE-8034-00AA006009FA}’ failed due to the following error: No such interface supported (Exception from HRESULT: 0×80004002 (E_NOINTERFACE)).”

After a little research, I found several pages with different solutions to the problem. A common thread is that it seems to involve SourceGear Vault Client (source control software). I suspect that this is only a problem for people who are using old versions of it (I’m using the spectacularly old version of 2.0.6!).

The solution which finally worked for me was to copy the Vault client folder, uninstall Vault, copy it back and make manual shortcuts. Then, in order to register it as a source control provider, I used the following registry file: -
Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\SourceGear\Vault Client]
"SCCServerName"="SourceGear Vault Client"
"SCCServerPath"="C:\\Program Files (x86)\\SourceGear\\Vault Client\\VaultIDE.dll"

To use a registry file, you need to copy and paste the code into a new notepad file and save it with a .reg extension. When you double click on it, Windows will ask if you want to add it to the registry. You may need to change your SCCServerPath before saving the file.

Thanks to Henrik Bruun’s post on this page for the registry fix.

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I’ve not been posting much on this blog recently because I’ve been very absorbed in a big project and been working crazy hours to get the coding done.

I should explain that this post is not about record locking to prevent concurrent update problems.  This is about being able to put a more permanent lock on a record in order to stop updates being made to it until the lock is removed.

The project that I’ve been working on has some shared records in a few tables that are used by a large number of other records in other tables.   The problem is that something was overwriting these shared records, which was pretty disasterous.  I managed to resurrect the data, which wasn’t such a problem, but I was very worried about how to stop it happening again, since these records are accessed in a number of different places.

The obvious first step was to audit the code and check for what was doing it.  I did that and identified some likely suspects and built in some code to prevent it happening again, but I wanted more reassurance than that, so I decided to try to get SQL Server itself to enforce a lock on them.  The solution that I came up with was to use a trigger.

The code of the trigger is as follows

CREATE trigger [dbo].[trgEnforcePersonLock] ON [dbo].[Person]
for UPDATE
AS
BEGIN
	if (select count(*) From deleted WHERE Locked=1)>0 AND (select count(*) From inserted WHERE Locked=1)>0
	begin
		rollback transaction
		raiserror('Cannot modify a locked person!',16,1)
	end 

END

The inserted virtual table contains the new data and the deleted virtual table contains the old. I’m checking that the update isn’t unlocking it, because otherwise we’ll never be able to! It works by checking whether the record is locked and if so, rolling back the transaction and raising an error. From testing, it looks like it works pretty well!

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In order to get around this problem, you need to take the following steps: -

First of all, configure Visual Studio so that you can launch the test server manually as follows: -

Under the Tools menu, select External Tools.
Add a new entry
Call it something like ASP.NET Development Server
Command is C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\WebDev.WebServer.EXE (you may need to alter the path for your local machine)
Arguments are /port:80 /path:$(ProjectDir) (note that you will need to leave a space on the end of this for it to work properly.  Also, you can change the port number if you wish)

Press OK.  You can now launch the development server from the new entry on your Tools menu.  This will show in your system tray.  You should probably remember to close it when you are done.

The next step is to configure your project to use the server.  Right click on your project and click Property Pages.  If an empty dialogue comes up, press cancel and repeat the process – it should work second time.  Under Start Options, select Use custom server and leave the Base URL blank.  You may wish to change the start action as well.

Once you are done, you can press F5 to start debugging.  Don’t forget that next time you open the project you will need to start the server from the tools menu before you start debugging again, otherwise it won’t work.

Also, bear in mind that if this is a copy of a remote site, things like database connection strings may need changing.  Don’t forget to be careful not to overwrite any settings when you copy back if that is the case!

If you do want to develop on a copy of the site, the Website menu has a useful option to Copy website.

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I recently found that 1&1 are doing some very nice Windows 2008 x64 Servers with 100MB connections, no explicit bandwidth cap and they come with Parallels Plesk Panel, which is pretty much the industry standard control panel for Windows.  I’m still in the process of setting this up at the moment, and I have had a couple of annoyances from Windows 2008 x64, but that isn’t really 1&1’s fault.  They have been quite helpful and seem pretty eager to help, unlike Fasthosts who pretty much just said it was my fault whenever I reported a problem.

The main disadvantage of using 1&1 that I can see is that their datacentres are in Germany.  The connection speed is perfectly good, but from the point of view of Google Local Search, this can be a little annoying as Google can mis-identify the country of a website.  However, as far as I understand, Google checks the domain extension first (so if it is .uk it should be ok), and then if it can’t identify it from that, you can still override the IP check using Google Webmaster Tools.

Anyway, although I haven’t started using it properly, and I have been getting a bit annoyed with Windows 2008 x64, it does seem like a pretty good deal and I’m very happy with what I’ve seen so far.  Oh yeah… they also have an affiliate program which is quite good

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Novell have been working on a project called Mono over the last few years to create an alternative implementation of .NET for other platforms, including Linux.  They have implemented most of the major features and classes, but there are still a few areas which are patchy.  I usually find that the Handles VB.NET keyword doesn’t work and causes a compiler error, but it is quite possible to make a decent site that operates on Mono.  I’ve even compiled a DLL file in Visual Studio and used it in a Mono project’s Bin folder.  Of course if you do that, you have to be careful only to reference classes which are available in Mono.

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After a bit of research, I found that Microsoft no longer support FrontPage Server Extensions in Windows Server 2008 as they have replaced it with WebDAV, which seems technically much better.  The problem is that WebDAV isn’t supported directly by Visual Studio (please sort that out Microsoft!), so the only way of using that is to use WebDAV Redirector so that you can map a network drive for the folder and then access the network drive from Visual Studio.  This is not really a practical solution for me as I would have dozens of sites to keep track of and I don’t have the patience to remap them when I need them or keep track of so many different drive letters!

A quick hunt around online for an alternateive gave me Ready to Run Software’s site, which frankly looks suprisingly unprofessional if you believe that they are actually working with Microsoft.  I don’t know whether they are or not, but they do seem to be the sole supplier of a ported version of FrontPage Server Extensions for Windows Server 2008.

All credit to them, their port of it does seem to work, although I did get an error “unable to read configuration for Microsoft Internet Information service” when I tried to install it, but their FAQ deals with that.  I managed to get it working, although it is a real pain in the neck that you have to be logged in as Administrator and not just an administrator!

The problem I had was managing the FrontPage settings for the website itself – I wanted to add another user.  I couldn’t seem to log in to the site admin – it wouldn’t authenticate me whatever username I used or whoever I made the web administrator.   The only solution I found was to use owsadm.exe, which took a bit of hunting around for how to do it.

First of all, I found it in C:\Program Files (x86)\Common Files\microsoft shared\Web Server Extensions\50\bin\

Secondly, I needed to work out how to call it.  It isn’t very well documented, but you need to do something like this…

owsadm -o roleusers -c add -u username -m domainname -web /subweb -name Admin

replace username and domainname as appropriate, and /subweb with the path to the subweb that you want to add the user to.  That can just be / for the root web.  You can replace Admin if you don’t want to use the administrative role for your new user.  I’m not sure what the other role names are.

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