How do you manage multiple versions of the same software for each customer?

Question

I have source code that is 95% the same for all customers. Some customers ask for something specific, however. How can I manage this, is it possible with VisualSVN/Subversion?

Update:

Some details about the application, it's a web ASP.NET MVC with NHibernate.

The application has several projects : the web part, the repo part (where we use NHibernate to access database) and a service project.

The service project uses the repo project and the service project is the project with business rules.

Answer 1

I can think of two approaches that might work.

The first involves branching the code for each customer. Any edit you make in the main line can then be integrated into the specific customer's branch when it's needed. Similarly if something in the core product is fixed in a branch it can be merged back into the main line for subsequent propagation to the other customers' branches. While this might seem the best approach it can be hard to maintain and keeping track of which branch has which edits will get fraught.

The second, and perhaps better approach, involves refactoring your code so that the customer specific code is in a single assembly - one per customer. This is then configured, perhaps by using dependency injection, when the product is installed. This way you only have one code line and no merging between branches. Though it does rely on the customer specific code being easily separated out.