Maintaining two versions of a business class library

Question

Our core business application uses a library (C# project) of business objects. Data access is done using the Wilson O/R Mapper (we're migrating to NHibernate this summer). The application has 3 front-end UIs: Windows Forms, ASP.NET, and a Windows Forms app that is installed on tablet PCs. The three front-ends perform different functions but they all access a core subset of the business classes.

The tablet PC application is the problem. We try to limit the amount of data pushed to the tablets to reduce the time it takes them to sync using SQL Server merge replication. The problem we've run into is when we add new functionality to the main application that we have no need to distribute to the tablet PCs or, if it's sensitive data, a strong need to not distribute it. Some of this can be controlled through replication, but we occasionally introduce dependencies in the core business objects that must be present in order for the O/R mapper to work.

Ideally, we would have two versions of the core business object library, Full and Compact. This seems like it would be a maintenance nightmare. Are there any strategies for managing this? Or alternatives? How does Microsoft manage the full and compact .NET Frameworks?

Answer 1

One thing you may be able to do is if you can compile for each platform seperately you may be able to use compiler directives to limit what is needed by the Tablet PC platform. However with you using an OR mapper that may prove to be difficult.

Now in an ideal world you would actually have your Domain objects (the ones that map to the OR) with very very little business logic shared. Then have a BO layer that consumes these Domain objects. If you managed to break out your code base this way you could in theory then have just seperate layers you need to deploy depending on your need.

However it sounds to me more like you need to perform an intelligent split.

What you probably need to do is segment your code such that the Tablet PC BO are in the core root BO asseymbly. Then have a BO extension assembly that has the additional objects, rules, etc that are needed for the Winform / Web app versions.

So while you would have two domain level business object components at this point you would not actually have any duplication. As your Tablet PC BO object would also be the base for the Winform / Asp.net app. Then the extension dll would only contain the extras needed for the bigger versions of hte applications.

If you followed this approach it might make things easier to manage. Just look at it from the Common stuff needed everywhere and the specialized approach. :)

I can go into much greater detail if you want, just wanted to give you a basic hit.

Answer 2

Your question talks about Tablet PC, which is really just XP and therefore the CF really isn't relevant, but for the sake of the question subject itself we can still talk about maintaining code used by the CF and the FFx (assuming you actually meant Windows Mobile or Windows CE).

First thing to know is that CF assemblies are retargetable. This means that a CF assembly can be directly used by a full-framework app without any recompiling (assuming it doesn't use any device specific stuff like P/Invoking coredll witout checking the runtime environment, using the WindowsMobile namespace, etc).

If using retargeting doesn't get you all the way there, then you can deal with the maintennace using compiler directives as well as partial classes. Daniel Moth covers tips on these quite well in his MSDN article.