Too many projects increase both the load and build time of your solution. Also a solution will take longer to start executing in debug due the overhead of loading/resolving multiple assemblies with associated PDB’s and symbols. This has an impact on the fast feedback loop we should strive to achieve. When I write code I want feedback as fast as possible. This includes compiling, and executing tests. Solutions with multiple projects affect the fast feedback loop.
Logical boundary != Physical boundary
An assembly is a unit of deployment in .Net. A Visual Studio project has a 1 on 1 relation with an assembly. We should have boundaries in our solutions, but we should not confuse logical boundaries with physical boundaries. A project in Visual Studio creates a physical boundary; this is often needed, but also open to abuse. Physical boundaries are all about deployment and versioning. If you are not deploying and versioning a part of your code independently, there is no reason to create a physical boundary. Multiple layers != multiple assemblies.
I don't want to reference System.Web across all code, so I create a separate assembly where I "isolate" the code that depends on that assembly. When I hear this argument, most of the time it equates to distrust among team members. Or, I don't trust other developers, so to avoid them referencing System.Web on business classes, I segregate them in another project that does not reference System.Web. Can you hear yourself? There may be a compelling reason to isolate a dependency in a separate assembly, but the reason should not be: to avoid other developers making a mess.
How do I do it?
My solutions start with two projects one for production code and one for tests. The question to ask before creating a project is: Do I need to deploy and version this part of the code independently? Only if the answer is yes do I create a new project.
This subject has been discussed in the community for a long time but I still don’t see any change. I’m continuously faced with solutions with dozens even hundreds of projects. In fact I would say this is the norm, unfortunately. I still see shocked faces, when I propose rearranging a solution using folders and namespaces instead of projects. So I’m adding my voice to other voices.
Some authors propose a number between 15-20 maximum projects in a Visual Studio Solution to be a good compromise. I disagree; my proposal is one for production code and a separate project for tests. Adding any other project to a solution should be considered very carefully.
Thanks to Tom Male and Eric Li Koo for reading drafts of this.