scanning.rst

Assembly Scanning

Autofac can use conventions to find and register components in assemblies. You can scan and register individual types or you can scan specifically for Autofac modules <../configuration/modules>.

Scanning for Types

Otherwise known as convention-driven registration or scanning, Autofac can register a set of types from an assembly according to user-specified rules:

csharp

var dataAccess = Assembly.GetExecutingAssembly();

builder.RegisterAssemblyTypes(dataAccess)

.Where(t => t.Name.EndsWith("Repository")) .AsImplementedInterfaces();

Each RegisterAssemblyTypes() call will apply one set of rules only - multiple invocations of RegisterAssemblyTypes() are necessary if there are multiple different sets of components to register.

Autofac also supports assembly scanning for open generics using RegisterAssemblyOpenGenericTypes(). This uses the same general semantics as RegisterAssemblyTypes():

csharp

var dataAccess = Assembly.GetExecutingAssembly();

builder.RegisterAssemblyOpenGenericTypes(dataAccess)

.Where(t => t.Name.StartsWith("MessageHandler")) .AsImplementedInterfaces();

Filtering Types

RegisterAssemblyTypes() and RegisterAssemblyOpenGenericTypes() each accept a parameter array of one or more assemblies. By default, all concrete classes in the assembly will be registered. This includes internal and nested private classes. You can filter the set of types to register using some provided LINQ-style predicates.

In 4.8.0 a PublicOnly() extension was added to make data encapsulation easier. If you only want your public classes registered, use PublicOnly():

csharp

builder.RegisterAssemblyTypes(asm)

.PublicOnly();

To apply custom filtering to the types that are registered, use the Where() predicate:

csharp

builder.RegisterAssemblyTypes(asm)

.Where(t => t.Name.EndsWith("Repository"));

To exclude types from scanning, use the Except() predicate:

csharp

builder.RegisterAssemblyTypes(asm)

.Except<MyUnwantedType>();

The Except() predicate also allows you to customize the registration for the specific excluded type:

csharp

builder.RegisterAssemblyTypes(asm)

.Except<MyCustomizedType>(ct =>

ct.As<ISpecial>().SingleInstance());

Multiple filters can be used, in which case they will be applied with logical AND.

csharp

builder.RegisterAssemblyTypes(asm)

.PublicOnly() .Where(t => t.Name.EndsWith("Repository")) .Except<MyUnwantedRepository>();

Specifying Services

The registration syntaxes for RegisterAssemblyTypes() and RegisterAssemblyOpenGenericTypes() are a subset of the registration syntax for single types <index>, so methods like As() all work with assemblies as well:

csharp

builder.RegisterAssemblyTypes(asm)

.Where(t => t.Name.EndsWith("Repository")) .As<IRepository>();

Additional overloads to As() and Named() accept lambda expressions that determine, for a type, which services it will provide:

csharp

builder.RegisterAssemblyTypes(asm)

.As(t => t.GetInterfaces()[0]);

As with normal component registrations, multiple calls to As() are added together.

A number of additional registration methods have been added to make it easier to build up common conventions:

Method	Description	Example
AsImplementedInterfaces()	Register the type as providing all of its public interfaces as services (excluding IDisposable).	builder.RegisterAssemblyTypes(asm) .Where(t => t.Name.EndsWith("Repository")) .AsImplementedInterfaces();
AsClosedTypesOf(open)	Register types that are assignable to a closed instance of the open generic type.	builder.RegisterAssemblyTypes(asm) .AsClosedTypesOf(typeof(IRepository<>));
AsSelf()	The default: register types as themselves - useful when also overriding the default with another service specification.	builder.RegisterAssemblyTypes(asm) .AsImplementedInterfaces() .AsSelf();

Scanning for Modules

Module scanning is performed with the RegisterAssemblyModules() registration method, which does exactly what its name suggests. It scans through the provided assemblies for Autofac modules <../configuration/modules>, creates instances of the modules, and then registers them with the current container builder.

For example, say the two simple module classes below live in the same assembly and each register a single component:

csharp

public class AModule : Module { protected override void Load(ContainerBuilder builder) { builder.Register(c => new AComponent()).As<AComponent>(); } }

public class BModule : Module { protected override void Load(ContainerBuilder builder) { builder.Register(c => new BComponent()).As<BComponent>(); } }

The overload of RegisterAssemblyModules() that does not accept a type parameter will register all classes implementing IModule found in the provided list of assemblies. In the example below both modules get registered:

csharp

var assembly = typeof(AComponent).Assembly; var builder = new ContainerBuilder();

// Registers both modules builder.RegisterAssemblyModules(assembly);

The overload of RegisterAssemblyModules() with the generic type parameter allows you to specify a base type that the modules must derive from. In the example below only one module is registered because the scanning is restricted:

csharp

var assembly = typeof(AComponent).Assembly; var builder = new ContainerBuilder();

// Registers AModule but not BModule builder.RegisterAssemblyModules<AModule>(assembly);

The overload of RegisterAssemblyModules() with a Type object parameter works like the generic type parameter overload but allows you to specify a type that might be determined at runtime. In the example below only one module is registered because the scanning is restricted:

csharp

var assembly = typeof(AComponent).Assembly; var builder = new ContainerBuilder();

// Registers AModule but not BModule builder.RegisterAssemblyModules(typeof(AModule), assembly);

IIS Hosted Web Applications

When using assembly scanning with IIS applications, you can run into a little trouble depending on how you do the assembly location. (This is one of our FAQs <../faq/iis-restart>)

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:

csharp

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.