Compile Time View Validation in ASP.NET MVC

  • June 17, 2016

Open up your favorite .cshtml file, put the mouse cursor in the middle of some razor code, and have a cat walk across your keyboard. If you don’t have a cat nearby, rolling your face on your keyboard will also suffice. You should start seeing things highlighted and underlined in red. Now go ahead and build your project.

Build Succeeded – Really?

Unlike all the other code in your project, your view files are not compiled when you hit the Build button in your IDE. Instead, they are compiled on-demand by IIS the first time someone tries to access them – dynamically being turned into an alpha-numerically named DLL. The problem is that any errors you have in your views won’t be made apparent until IIS tries to compile them, at which point the user who requested the view would see an error page. So how do you protect yourself from this happening?

Pre-compilation To The Rescue

Pre-compiling Razor views is possible, there are projects out there that will allow you to turn your views into DLL files before they even touch an IIS server. However doing so in this case would be overkill, we just want to know if there are obvious errors in our views.

To let you find those compile-time bugs there’s a flag you can set in your .csproj file.

<MvcBuildViews>true</MvcBuildViews>

This will cause your views to be test compiled when your project is built. Why do I emphasize test compiled? Because they aren’t compiled in the traditional sense that you end up with resulting DLL files, they will still need to be dynamically compiled by IIS later on. It’s just a test to see if when they are compiled by IIS, if any errors will be thrown.

You will find that this setting is false by default, and there’s a good reason for that – view compilation takes time. In a large enough project it could take enough time to seriously annoy a developer who is used to those quick compiles. A medium sized project of around 70 views has the compile time grow by 36 seconds when this feature is enabled.

But there’s a compromise, instead of having your views test compile during every build, we can set it to only test compile when performing a release build. If you look in your .csproj file, you will find a PropertyGroup block for each build configuration in your project. Find your release build configuration and add the MvcBuildViews property. In this example my build configuration is simply called Release.

<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
    <MvcBuildViews>true</MvcBuildViews>
    ...
</PropertyGroup>

This way the debug builds you do on your machine will run fast, while the builds that run on your build server will take a bit longer, while validating that all your views will compile. If a view can’t be compiled, the build fails, and the code will never be deployed to an IIS server.

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