NServiceBus: Could not enumerate all types

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I’ve recently started using NServiceBus for the first time in a long time.  The initial setup was great, but once I started integrating it into a really large, complex, existing app, it took a bit of re-working.  One of the errors I ran into was a HUGE string of errors all centering around not being able to enumerate all types.  In this case, the root cause turned out to be NServiceBus scanning every single .dll of your app looking for handlers.  By default, it searches everything, and when that happens it can run into situations where it can break.  The out of the box, greenfield developer experience works great, but if you’re adding NServiceBus to an existing app, then you need to add the line below to fix the error.

Basically in an existing app where you’ve added NServiceBus code to handle/send messages, then you know exactly the assembly where it lives.  Again, by default, NServiceBus scans everything, so in NServiceBus 5.0 and above, when you create the actual Bus object, you need to specify in the configuration the assemblies you want to scan.  Generally, the code is going to be in right int he webapp/console app that you are adding it to, so in that case just add:

var config = new BusConfiguration();

// config.AllYourOtherConfigurationGoesHere

config.AssembliesToScan(Assembly.GetExecutingAssembly());

var bus = Bus.Create(config);

This tells NServiceBus to only scan the assembly that is currently in use (This will fix things 95% of the time, unless your comsumer/sender code is in a different project and pulled in).  Once this is configured, NServiceBus will not scan every single assembly in hopes of finding a handler somewhere, which helps a ton if you have really old assemblies that are fragile and busted.  :)

Ryan Hayes

Ryan is a Microsoft MVP award winner with over eight years of software experience, working with big-name clients such as Discovery Channel, AOL, Toyota, and the National Academy of Sciences. Ryan has helped teams deliver award-winning applications that drive business processes, site traffic, and profit, putting his experience and creativity to work to build amazing solutions for the enterprise web, desktop and mobile platforms.