Autofac method level interception with Castle DynamicProxy in .NET Core 2

Question

I currently wrote an Interceptor which code is below

public class TransactionalInterceptor : IInterceptor
{
    public void Intercept(IInvocation invocation)
    {
        using (var transaction = ...)
        {
            try
            {
                invocation.Proceed();
                transaction.Commit();

            }
            catch
            {
                transaction.Rollback();
            }
            finally
            {
                transaction.Dispose();
            }
        }

    }
}

but when register this interceptor it will apply to all methods. I have a service class with a repository injected having CRUD methods. I don't want a transaction to be opened for query methods.

I read this link but I cannot figure out how to apply it to my code http://docs.autofac.org/en/latest/advanced/adapters-decorators.html#decorators

I don't know who to refactor my TransactionalInterceptor (and register it) to use it in a class like this code

[Intercept(typeof(LoggerInterceptor))] //logger
public class SomeService : ISomeService
{
    private readonly ISomeRepository someRepository;

    public SomeService(SomeRepository someRepository)
    {
        this.someRepository = someRepository;
    }

    public IEnumerable<SomeDto> GetAll()
    {
        // code
    }

    public SomeDto GetById()
    {
        // code
    }

    [Transactional]
    public int Create(SomeDto someDto)
    {
        // code to insert
    }
}

Answer 1

also can try, it is simple https://fs7744.github.io/Norns.Urd/index.html

public class AddTenInterceptorAttribute : AbstractInterceptorAttribute
{
    public override void Invoke(AspectContext context, AspectDelegate next)
    {
        next(context);
        AddTen(context);
    }

    private static void AddTen(AspectContext context)
    {
        if (context.ReturnValue is int i)
        {
            context.ReturnValue = i + 10;
        }
        else if(context.ReturnValue is double d)
        {
            context.ReturnValue = d + 10.0;
        }
    }

    public override async Task InvokeAsync(AspectContext context, AsyncAspectDelegate next)
    {
        await next(context);
        AddTen(context);
    }
}


[AddTenInterceptor]
public interface IGenericTest<T, R> : IDisposable
{
    // or
    //[AddTenInterceptor]
    T GetT();
}

Answer 2

I solved the problem with ProxyGenerationHook. See the answer

1. Create your custom attribute for selecting which method to intercept. This attribute's target should be Method.

    [System.AttributeUsage(AttributeTargets.Method, Inherited = true, AllowMultiple = true)]
    sealed class UseInterceptorAttribute : Attribute
    {
        public UseInterceptorAttribute()
        {
        }
    }

2. Create your service interface and service class:

    public interface ISomeService
    {
        void GetWithoutInterceptor();

        [UseInterceptor]
        void GetWithInterceptor();
    }

    public class SomeService
    {
        void GetWithoutInterceptor()
        {
            //This method will not be intercepted...
        }

        [UseInterceptor]
        void GetWithInterceptor()
        {
            //This method will be intercepted...
        }
    }

3. Create your ProxyGenerationHook

    public class SomeServiceProxyGenerationHook : IProxyGenerationHook
    {
        public void MethodsInspected()
        {
        }

        public void NonProxyableMemberNotification(Type type, MemberInfo memberInfo)
        {
        }

        public bool ShouldInterceptMethod(Type type, MethodInfo methodInfo)
        {
            return methodInfo
                .CustomAttributes
                .Any(a => a.AttributeType == typeof(UseInterceptorAttribute));
        }
    }

4. Don't use attributes for enabling interceptors. Enable it when registering your service like this:

    public class AutofacDependencyResolver
    {
        private readonly IContainer _container;
        public AutofacDependencyResolver()
        {
            _container = BuildContainer();
        }

        private IContainer BuildContainer()
        {
            var proxyGenerationOptions = new ProxyGenerationOptions(new ProductServiceProxyGenerationHook());

            builder.RegisterType<SomeService>()
                .As<ISomeService>()
                .EnableInterfaceInterceptors(proxyGenerationOptions)
                .InterceptedBy(typeof(TransactionalInterceptor))

            builder.Register(c => new TransactionalInterceptor());
            return builder.Build();
        }

        public T GetService<T>()
            where T:class
        {
            var result = _container.TryResolve(out T serviceInstance);
            return serviceInstance ?? throw new Exception($"The service could not found: {nameof(T)}");
        }
    }

This solution is following this article

Also I uploaded the minimal example about this solution.

Answer 3

The invocation parameter of the Intercept method contains a Method property which is a MethodInfo of the method currently intercepted.

You can use this property to do what you want.

For example by using the method name :

public void Intercept(IInvocation invocation)
{
    if (invocation.MethodInvocationTarget.Name != nameof(ISomeService.Create))
    {
        invocation.Proceed();
        return;
    }
    using (var transaction = ...)
    {
        try
        {
            invocation.Proceed();
            transaction.Commit();
        }
        catch
        {
            transaction.Rollback();
        }
        finally
        {
            transaction.Dispose();
        }
    }
}

or based on an attribute from the target method :

if (!invocation.MethodInvocationTarget
               .CustomAttributes
               .Any(a => a.AttributeType == typeof(TransactionalAttribute)))

You can also use the IInterceptorSelector type but it requires more work to register it with Autofac