Sunday, July 13, 2008

Don't make me GAC

We discovered an interesting "feature" in VisualStudio 2005 a couple days ago. Let's say I have a solution containing a Utilities project and a web site referencing that project. The Utilities assembly references a third-party dll (log4net in this case.) When the web site is compiled, it automatically pulls any dependent files into its 'bin' folder. Note the presence of log4net.dll

This seems fairly straightforward. But let's say I then load the solution on another computer (a build server perhaps.) The code compiles as before, but this time it doesn't pull in log4net.dll

At this point, I could manually copy the dll into the folder, right? That was my first thought, which of course proved to be wrong. The reason is that we also have an install project for the site. The installer is set to use all output files from the web project. If we add files to the site, the installer will automatically include them in the next compile. Unfortunately, when I manually add the dll to the bin folder, the installer overlooks it.

My next thought was to directly reference the log4net.dll in the web project.

Which still compiles on my box. And still ignores the dll on the build server. At this point, we opened up the references dialog on the build box. Much to our surprise, the dll is being referenced in the GAC

It seems that when a web project loads, it first looks in the GAC for referenced assemblies. If it finds them there, it ignores the files originally pointed to. Because of this, VisStudio doesn't copy the files to the bin folder. Which of course means the installer won't contain the dll.

Ideally, the dll shouldn't have been GAC'd on the build server. Since removing it from the GAC would cause us other issues, our workaround was to hard-code log4net.dll in the install project.

Note: The web site was built using the out-of-the-box project template, which doesn't create an actual .proj file. Microsoft later released a Web Application Project (with VS2005 SP1) that does create a .proj. It's possible that this would force the dll to load from the file reference, but I've not tested that theory.

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