Autofac Dependency Resolver ocasionally crash on controller resolving mvc 5 (DependencyResolutionException) - dependency-injection

Question

i have following problem, I have web application in mvc5 with autofac dependency injection and generic data repositories. Usually all is working fine, the web is runing with no error, but after some time online following error appear:
The dependency resolver is folowing:
public class IoCConfig {
public static IContainer BuildContainer < T > () {
ContainerBuilder builder = new ContainerBuilder();
builder.RegisterApiControllers(typeof(T).Assembly);
builder.RegisterControllers(typeof(T).Assembly);
try {
foreach(var type in AssemblyLoader.Load < IDependency > ()) {
var registration = builder.RegisterType(type);
foreach(var interfaceType in type.GetInterfaces().Where(itf => typeof(IDependency).IsAssignableFrom(itf))) {
registration = registration.As(interfaceType);
if (typeof(IUnitOfWorkDependency).IsAssignableFrom(interfaceType)) {
registration = registration.InstancePerRequest();
}
}
}
} catch (Exception ex) {
throw ex;
}
return builder.Build();
}
}
and is executed on Application_Start.
The example constructor of the controller is:
[Authorize]
public class ClassesManagmentController: Controller {
IDepartmentsRepository _departmentRepo;
IClassesRepository _classesRepo;
IClassesCategoriesRepository _classesCategoriesRepo;
public ClassesManagmentController(IDepartmentsRepository departmentsRepo,
IClassesRepository classesRepo,
IClassesCategoriesRepository classesCatiegoriesRepo) {
_departmentRepo = departmentsRepo;
_classesRepo = classesRepo;
_classesCategoriesRepo = classesCatiegoriesRepo;
}
// the rest of the Controller code
}
And the example repo interface and class are:
public class ClassesCategoriesRepository: Bases.RepositoryBase < ClassesCategoryDto > , IClassesCategoriesRepository {
public ClassesCategoriesRepository(IContextFactory factory): base(factory) {
}
}
public interface IClassesCategoriesRepository: IGenericRepository < ClassesCategoryDto > , IDependency {}
The repositories are in dedicated project, the dependency resolver and identification interfaces (IDependency) are in dedicated project, and web is in one more project.
I checked already twice if all projects of my solution are referencing the same autofac and mvc libraries. i was trying different resolving types but i dont found solution yet.
Any help will be appreciated.

Answer 1

If things are working for a while and then stop working chances are IIS is recycling the app pool and your assembly scanning mechanism isn't picking up all the assemblies correctly. Per the documentation:
When hosting applications in IIS all assemblies are loaded into the AppDomain when the application first starts, but when the AppDomain is recycled by IIS the assemblies are then only loaded on demand.
To avoid this issue use the GetReferencedAssemblies() method on System.Web.Compilation.BuildManager to get a list of the referenced assemblies instead:
var assemblies = BuildManager.GetReferencedAssemblies().Cast<Assembly>();
That will force the referenced assemblies to be loaded into the AppDomain immediately making them available for module scanning.
If this controller never works but everything else does, do a test in one of the working controllers - try to manually resolve the IDepartmentsRepository and see if you can. If you can, then... strange things are afoot. But if you can't, then it means that particular repo isn't being picked up by the scanning and isn't registered, so the exception is telling you exactly what's wrong.