Jelle Druyts

Tough luck. I had been busy (well, "busy", as I mentioned: the summer has been a bit of an idle time tech-wise) writing an article on the all-new Profile concept in ASP.NET 2.0, but I just noticed that I've been pre-empted by MSDN where the article "Storing User Information with ASP.NET 2.0 Profiles" just went online. It's a great read though, and it covers pretty much everything I had to say about it (and more of course) except the part about Profile migration on which I'll add my 2 cents now.

Let me just briefly summarize the Profile, which is one of the cornerstones of the new Personalization framework: the Profile is a "personal, type-safe, persistent data store" for each of your website's users. You can use it to remember settings (like language or culture, UI theme, ...), data (favorite color, shopping cart items, ...) or anything else you can think of really. Type-safety is ensured because it is an actual object with typed properties, and the data is automatically persisted into a data store of your choice ^[1]. Furthermore, you can configure the Profile to work for users that aren't known or logged in yet. When the user decides he likes your site so much that he wants to create an account, you can migrate his anonymous profile very easily in Global.asax by implementing a method like the following one:

Sub Profile_MigrateAnonymous(ByVal s As Object, ByVal e As ProfileMigrateEventArgs)
    
    ' Fish up the profile belonging to the anonymous user that just logged in.
    Dim anonProfile As HttpProfile = Profile.GetProfile(e.AnonymousId)
    
    ' Move the settings over to the authenticated user's profile.
    Profile.FavoriteColor = anonProfile.FavoriteColor

End Sub

So far for the article's example. There's a little issue with this approach though. Imagine a user who already created an account and is now just browsing to your site. He hasn't logged in yet so he gets the default settings for an anonymous user. Then he logs in, thereby migrating and overwriting his own settings (which were persisted from last time) with the default ones. Too bad, you just lost your shopping cart.

Unfortunately, there's currently no way of checking if the profile being migrated to is new - i.e. if the user already had an account and is now just logging in, or if he just created an account. Only in the latter case will you want to migrate the profile, so that's pretty tricky. Hence the following feature suggestion: provide a ProfileMigrateEventArgs.IsProfileNew flag so we can check if we actually need to migrate the profile.

Another option would be to check on the default values of the profile ^[2]. But what if the user changed one of the properties before he logged in? You would wrongfully not migrate his settings. Not good.

So until there's a better way of doing this, I'd suggest putting a flag on the Profile itself that says it's a new profile and flip it over once you've migrated the anonymous profile, e.g.:

<profile>
 <properties>
  <add name="FavoriteColor" allowAnonymous="true" defaultValue="Red" />
  <add name="HasMigrated" type="System.Boolean" defaultValue="false" />
 </properties>
</profile>

Sub Profile_MigrateAnonymous(ByVal s As Object, ByVal e As ProfileMigrateEventArgs)
    
    ' Migrate the profile preferences only if the user is new.
    If Not Profile.HasMigrated Then
    
        ' Fish up the profile belonging to the anonymous user that just logged in.
        Dim anonProfile As HttpProfile = Profile.GetProfile(e.AnonymousId)
    
        ' Move the settings over to the authenticated user's profile.
        Profile.FavoriteColor = anonProfile.FavoriteColor
        
        ' Indicate that migration has been done.
        Profile.HasMigrated = True

    End If
    
End Sub

One last remark about the Profile: a VaryByProfileProperty option for output caching would make sense. Imagine you have a multilingual website and you keep the user's Culture setting in the Profile. Then you could easily configure your page to be cached for all users that share the same culture as such:

<%@ OutputCache Duration="60" VaryByProfileProperty="Culture"  %>

It's not really shocking but it's just a bit easier than using VaryByCustom and returning the Culture manually...

[1] The Profile derives from the System.Configuration.SettingsBase, which is the new configuration system available in .NET 2.0. It's also used in Windows Forms so you can have type-safe access to application- and usersettings in this environment as well. Goodness!

[2] If you're working in VB.NET, you might wonder how you can access the default value of a Profile property. It's not listed in IntelliSense (I'm still puzzled why not because it does show up if you use C#) but there's a Properties collection you can use to access a certain Profile property and get the default value out of it as follows:

Dim defaultValue As Object = Profile.Properties("FavoriteColor").DefaultValue