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By default SharePoint will use impersonation, so the web.config file will have the setting:

<identity impersonate="true" />

This means that if you try and connect to a SQL server database from say a custom web part, the connection will appear to SQL server as the user that requested the page. This is very useful if you care about the actual user, so for example if the database has permissions set based on this assumption.

However it is often useful to have just the application pool account connect to the SQL Server database or you may wish to give the application pool account permissions to connect to active directory but not every user.

It this case you will need to impersonate the application pool account. There is a bit of code floating around the web that uses P/Invoke to call ReverToSelf() from the advapi32.dll. It turns out it’s simpler than that:

using (HostingEnvironment.Impersonate()) 

{

    // access external resource as app pool account

}

The HostingEnvironment.Impersonate() will do the same thing that as a call to RevertToSelf().

If you like me and organise your data access calls into nice methods that perform a discrete action such as:

public static void DeleteUser(int userID)

{

//do some database access

}

You might be really loathed to wrap all these methods with the same code like:

public static void DeleteUser(int userID)

{

   using(HostingEnvironment.Impersonate())

   {

      //do some database access

   }

}

Instead you might like to take a look at what a project such as PostSharp can offer:

"You can make your own custom attributes that will really add new behaviors to your code! This is sometimes called aspect-oriented programming (AOP) or policy injection."

This means that you can define your own attribute that will have code that will run on any invocation of your code:

public class ImpersonateAttribute : OnMethodInvocationAspect

{

    public override void OnInvocation(MethodInvocationEventArgs eventArgs)

    {

        using(HostingEnvironment.Impersonate())

        {

            eventArgs.Proceed();

        }

    }

}

So our code then looks like this:

[ImpersonateAttribute]

public static void DeleteUser(int userID)

{

   //do some database access    

}

Much easier to maintain. Now every bit of code with this attribute will run as the application pool account.

I came across an interesting problem recently deploying an ASP.NET application to the ISV directory in CRM 4, the ASP.NET application was working fine using the Cassini web server inside of Visual Studio, but when it was deployed to the ISV directory on the CRM server it failed to run.

Basically any postback caused the web forms to loose all it’s current data, so things like dropdown lists would end up blank.

It was pretty obvious that this was caused by ViewState being turned off.

The default web.config file of CRM looks like:

<pages buffer="true" enableSessionState="false" enableViewState="false" validateRequest="false"/>

Since the ISV directory inherits from this web.config file, all the applications in the ISV directory will also have viewstate disabled.

So just add the following line to your web.config file in the ISV directory:

<pages enableViewState="true"/>

Personally I don’t really see the need to enable viewstate, in most cases it isn’t needed if the programmer understands it’s purpose, but sometimes your just trying to deploy code that someone else wrote.

A lot of functionality can be added to CRM with JavaScript, if your like me and do the bulk of your normal web development JavaScript with a toolkit like JQuery, you will quickly miss the power and ease of doing things without it. The good news is that it is pretty easy to load JQuery into the page:

var script = document.createElement('script');

script.type = 'text/javascript';

script.src = '/ISV/jquery.js';

script.onreadystatechange = function()

{

if(this.readyState == "complete" || this.readyState == "loaded")

   setupPage();

};

var head = document.getElementsByTagName('head')[0];

head.appendChild(script);

Now you can use the setupPage() function with all your familiar JQuery goodness.