I am using PostSharp - OnMethodBoundaryAspect in OperationContract. The aspect doesnt seem to fire though. I have the necessary reference to postsharp dll. Pseudo code below.
Aspect
[Serializable]
[MulticastAttributeUsage(MulticastTargets.Method, Inheritance = MulticastInheritance.Multicast)]
public class LoggingAspect : OnMethodBoundaryAspect
{
//Implementation for entry and exit
}
Usage
[ServiceContract]
public interface ITest
{
[OperationContract]
[LoggingAspect(.....)]
void Test();
}
Any help is deeply appreciated
We need to do the following
Install Postsharp through NuGet on the project which you want to write your custom aspect.
This will ensure that the targets are present in the .csproj files thereby enabling injection during compile time.
Install PostSharp though NuGet in all projects where you want to use the aspect which you wrote as mentioned in #1
Thanks AlexD and Daniel Balas for the inputs
Related
I would like to register the following items for DI using an open generic implementation and interface. I know the following example will not work, as well as other combinations I've tried with MakeGenericType, or GetGenericArguments. I would like to simply call AddRepository<MyDbContext> and then be able to inject my implementation into classes without explicitly having to register the type I am using.
Interface
public interface IRepository<TEntity>
{
}
Implementation
public class Repository<TEntity, TContext> : IRepository<TEntity>
where TEntity : class
where TContext : DbContext
{
}
Registration
public static class RepositoryServiceCollectionExtensions
{
public static IServiceCollection AddRepository<TContext>(
this IServiceCollection services) where TContext : DbContext
{
services.TryAddScoped(
typeof(IRepository<>),
typeof(Repository< , TContext>));
return services;
}
}
The dependency injection container Microsoft.Extensions.DependencyInjection and its abstraction layer does not support open generic factories. So you generally cannot achieve what you would like to do there. There’s also no support planned.
Unlike many those other dependency injection related features, this is also not really possible to patch by just providing the right wrapper or factory types. So you will actually have to change your design here.
Since you want to resolve IRepository<TEntity> and the only way to do this is by registering an equivalent open generic type, you will have to have some type Repository<TEntity> that implements your repository. That makes it impossible to retrieve the database context type from the generic type argument, so you will have to use a different way here.
You have different options to do that. For example, you could configure your Repository<TEntity> (e.g. using M.E.Options) with the context type and make that resolve the Repository<TEntity, TContext> dynamically. But since you have actual control over your database context, I would suggest either adding a marker interface or introducing another type for the context which you can then register with the container:
public class Repository<TEntity> : IRepository<TEntity>
{
public Repository(IDbContext dbContextFactory)
{ … }
}
public class MyDbContext : DbContext, IDbContext
{ … }
Then, your extension method could look like this:
public static IServiceCollection AddRepository<TContext>(this IServiceCollection services)
where TContext : DbContext, IDbContext
{
services.AddTransient(typeof(IDbContext), sp => sp.GetService<TContext>());
services.TryAddScoped(typeof(IRepository<>), typeof(Repository<>));
return services;
}
Of course, this changes how your Repository implementation works, but I don’t actually assume that you need to know the TContext type other than to inject the database context type. So this will probably still work for you.
That being said, I have too agree with Chris Pratt, that you probably don’t need this. You say that you want to introduce the repository, because “coding stores and implementations for every entity is a time consuming task” but you should really think about whether you actually need that. A generic repository is very limited in what it can do, and mostly means that you are doing just CRUD operations. But exactly that is what DbContext and DbSet<T> already do:
C: DbContext.Add, DbSet<T>.Add
R: DbContext.Find, DbSet<T>.Find
U: DbContext.Update, DbSet<T>.Update
D: DbContext.Remove, DbSet<T>.Remove
In addition, DbContext is a “unit of work” and DbSet<T> is an IQueryable<T> which gives you a lot more control and power than a generic repository could possible give you.
You cannot have a partially open generic reference. It's all or nothing. In other words, you can try:
services.TryAddScoped(
typeof(IRepository<>),
typeof(Repository<,>));
But, if that doesn't work, you'll likely need to add a type param to your AddRepository method:
public static IServiceCollection AddRepository<TEntity, TContext>(this IServiceCollection services)
where TEntity : class
where TContext : DbContext
{
services.TryAddScoped(
typeof(IRepository<TEntity>),
typeof(Repository<TEntity, TContext>));
return services;
}
Of course, I think that breaks what you're ultimately trying to achieve here: registering repositories for all the entity types in one go. You can always use a bit of reflection find all entities in your assembly (they would need to share something in common: base class, interface, etc.) and then enumerate over them and use reflection to call AddScoped on your service collection for each.
All that said, the best thing you can do here is to actually throw all this away. You don't need the repositories. EF already implements the repository and unit of work patterns. When you use an ORM like EF, you're essentially making that your data layer instead of a custom class library you create. Putting you own custom wrapper around EF not only adds entropy to your code (more to maintain, more to test, and more than can break), but it can also mess up the way EF works in many cases, leading to less efficiency in the best cases and outright introducing bugs into your application in the worst cases.
I'm in a situation where the implementation of a library we are using is newer than the implementation one of our dependencies was coded against. E.g. Dependency uses MyLibrary-1.0 and we're using MyLibrary-2.0.
In the newer implementation a deprecated method has been removed, which causes run-time errors for us.
I'm trying to use AOP (Spring-AOP to be specific) to intercept calls made to the missing method, and proxy them into an existing method... but I can't seem to get the Aspect right.
It feels like Java is raising the 'java.lang.NoSuchMethodError' exception before my Aspect has an opportunity to intercept. Is there some trick I'm missing, or is this just not feasible (e.g. the method must exist in order to aspect it)?
#Before("execution(* com.mylibrary.SomeClass.*(..))")
Fails with java.lang.NoSuchMethodError
#Around("target(com.mylibrary.SomeClass) && execution(* missingMethod(..))")
Fails with java.lang.NoSuchMethodError
Assuming that your are talking about a 3rd party library which is independent of Spring, you cannot use Spring AOP with its proxy-based "AOP lite" approach which only works for public, non-static methods of Spring components. Please use the more powerful AspectJ instead. The Spring manual explains how to integrate full AspectJ with load-time weaving (LTW) into Spring applications. If your application is not based on Spring so far and you just wanted to use the framework because of Spring AOP, you can skip the whole Spring stuff altogether and use plain AspectJ.
The feature you want to use is an inter-type declaration (ITD), more specifically AspectJ's ability to declare methods for existing classes. Here is some sample code:
3rd party library:
package org.library;
public class Utility {
public String toHex(int number) {
return Integer.toHexString(number);
}
// Let us assume that this method was removed from the new library version
/*
#Deprecated
public String toOct(int number) {
return Integer.toOctalString(number);
}
*/
}
Let us assume that the method I commented out was just removed from the latest version your own project depends on, but you know how to re-implement it.
Project dependency depending on old version of 3rd party library:
package com.dependency;
import org.library.Utility;
public class MyDependency {
public void doSomethingWith(int number) {
System.out.println(number + " in octal = " + new Utility().toOct(number));
}
}
Because the previously deprecated method Utility.toOct does not exist anymore in the version used by your own project, you will get NoSuchMethodError during runtime when calling MyDependency.doSomethingWith.
Your own application:
package de.scrum_master.app;
import org.library.Utility;
import com.dependency.MyDependency;
public class Application {
public static void main(String[] args) {
System.out.println("3333 in hexadecimal = " + new Utility().toHex(3333));
new MyDependency().doSomethingWith(987);
}
}
As you can see, the application also uses the same library, but a different method which still exists in the current version. Unfortunately, it also uses the dependency which relies on the existence of the removed method. So how should we repair this?
Aspect using ITD:
AspectJ to the rescue! We just add the missing method to the 3rd party library.
package de.scrum_master.aspect;
import org.library.Utility;
public aspect DeprecatedMethodProvider {
public String Utility.toOct(int number) {
return Integer.toOctalString(number);
}
}
If you compile this project with the AspectJ compiler Ajc, it just works. In your real life scenario, compile the aspect into its own aspect library, put the weaving agent aspectjweaver.jar on the JVM command line in order to activate LTW and enjoy how it weaves the method into the library class via byte code instrumentation during class-loading.
Log output:
3333 in hexadecimal = d05
987 in octal = 1733
Et voilà! Enjoy. :-)
When the JVM load a class, it resolves all dependencies in a "linker" phase : external classes, properties and method. You can't pass this phase in your case, because methods are missing.
There are two modes on (Spring-)AOP: Proxy, and weaving.
Proxy create... a proxy around a class: the targeted class must exist and be loaded
Weaving can happen before a class is loaded: when a classloader load a class, an array of byte[] is passed to the weaver, which can manipulate the class bytecode before the class is really reified. This type of aop can work in your case. However, it will not be an easy task.
I have my UnitOfWork class in DataAccess project and to resolve my IUnitOfWork interface (with UnitOfWork class), I need to use Ninject to Bind the IUnitOfWork interface with UnitOfWork class in my web project.
To do this I need to refer my DataAccess project (which contains UnitOfWork class) in the Web project. Is this good design wise? I mean referring DataAccess in the web project seems to be a bad idea & I never did that.
So, please advise me on what to do?
If you are not comfortable having reference to DataAccess project (imho it is not a big issue) you can create separate project (let's call it ModuleProject) that will contain NinjectModules. ModuleProject will have references to both DataAccess and to project where IUnitOfWork is defined. In your web project you will have reference to ModuleProject and use its classes to register modules.
Module
public class NinjectConfiguration : NinjectModule
{
public override void Load()
{
Bind<IUnitOfWork>().To<UnitOfWork>();
}
}
Registration in web project
kernel.Load(new Mod.NinjectConfiguration());
More information on modules here.
I am using the mvc mini profiler to profile a NUnit Test suite.
I am just curious whether it would be possible to use the mvc mini profiler's profiling mechanism as an aspect, i.e., rather than having those using statements could I not somehow just provide some attribute above the method I want to profile?
I know that this would kill the kind of granularity we get with the mini profiler but in some cases, it's just more appropriate to use the AOP approach.
Ideas? Suggestions?
Thanks a bunch.
You would need to weave in code, so you would have to look at either PostSharp, Roslyn or some other IL weaving mechanism.
Yes, it is totally possible. In my case I was using Autofac, which implements interception using Castle's DynamicProxy.
But a very basic interceptor for profiling would look something like this (in C#):
public class ProfilerInterceptor : IInterceptor
{
#region Implementation of IInterceptor
public void Intercept(IInvocation invocation)
{
using (MiniProfiler.Current.Step(invocation.TargetType.Name + "." + invocation.Method.Name))
{
invocation.Proceed();
}
}
#endregion
}
NOTE: I know your preference was weaving rather than interception through proxies, but I'm posting it in case anybody else finds it useful.
In the Head First Design Patterns book, the author often says that one should program to interface rather than implementation?
What does that mean?
Let's illustrate it with the following code:
namespace ExperimentConsoleApp
{
class Program
{
static void Main()
{
ILogger loggerA = new DatabaseLogger();
ILogger loggerB = new FileLogger();
loggerA.Log("My message");
loggerB.Log("My message");
}
}
public interface ILogger
{
void Log(string message);
}
public class DatabaseLogger : ILogger
{
public void Log(string message)
{
// Log to database
}
}
public class FileLogger : ILogger
{
public void Log(string message)
{
// Log to File
}
}
}
Suppose you are the Logger developer and the application developer needs a Logger from you. You give the Application developer your ILogger interface and you say to him he can use but he doesn't have to worry about the implementation details.
After that you start developing a FileLogger and Databaselogger and you make sure they follow the interface that you gave to the Application developer.
The Application developer is now developing against an interface, not an implementation. He doesn't know or care how the class is implemented. He only knows the interface. This promotes less coupling in code and it gives you the ability to (trough configuration files for example) easily switch to another implementation.
Worry more about what a class does rather than how it does it. The latter should be an implementation detail, encapsulated away from clients of your class.
If you start with an interface, you're free to inject in a new implementation later without affecting clients. They only use references of the interface type.
It means that when working with a class, you should only program against the public interface and not make assumptions about how it was implemented, as it may change.
Normally this translates to using interfaces/abstract classes as variable types instead of concrete ones, allowing one to swap implementations if needed.
In the .NET world one example is the use of the IEnumerable/IEnumerator interfaces - these allow you to iterate over a collection without worrying how the collection was implemented.
It is all about coupling. Low coupling is a very important property* of software architecture. The less you need to know about your dependency the better.
Coupling can be measured by the number of assumptions you have to make in order to interact/use your dependency (paraphrasing M Fowler here).
So when using more generic types we are more loosely coupled. We are for example de-coupled from a particular implementation strategy of a collection: linked list, double linked list, arrays, trees, etc. Or from the classic OO school: "what exact shape it is: rectangle, circle, triangle", when we just want to dependent on a shape (in old school OO we apply polymorphism here)