How to create an aspect decorator to handle EF transactions

Question

I'm working (maintaining) on a dll assembly that acts as a Data Access Layer, there are many methods that requires transaction handling, many other do not, it's a currently "functional" dll, without any transaction handling method, I need to add it, so I'm looking for an easy way to add a transaction handler.

I'm wondering if is it possible to use AOP to create a decorator that I can add to the methods that requires a transaction.

I would like to have something like this:

[Transaction]
void MyDbMethod()
{
  //DoSomething
  myContext.SaveChanges();  
}

For the EF model definition I'm using Code First, the current project uses Unity framework for some other DI tasks, can that framework be used for this?

Possibly look into this http://stackoverflow.com/questions/13211261/using-attributes-to-call-methods then you can check `System.Transactions.Transaction.Current != null` and decide to continue or not. — Wurd, Sep 15 '16 at 16:01

score 2 · Accepted Answer · answered Sep 15 '16 at 19:10

If someone faces this same issue, I did not found any "by hand" solution, instead I used the PostSharp library and its OnMethodBoundaryAspect class, but be careful, at this moment the free/express license has limitations about the amount of classes where you can use it, so read carefully its limitations.

using System.Transactions;
using PostSharp.Aspects;
using PostSharp.Serialization;

namespace MyProject
{
    [PSerializable]
    public class Transaction : OnMethodBoundaryAspect
    {
        public Transaction()
        {
            //Required if the decorated method is async
            ApplyToStateMachine = true;
        }

        public override void OnEntry(MethodExecutionArgs args)
        {
            //TransactionScopeAsyncFlowOption.Enabled => Required if the decorated method is async
            var transactionScope = new TransactionScope(TransactionScopeOption.Required, TransactionScopeAsyncFlowOption.Enabled);
            args.MethodExecutionTag = transactionScope;
        }

        public override void OnSuccess(MethodExecutionArgs args)
        {
            var transactionScope = (TransactionScope)args.MethodExecutionTag;
            transactionScope.Complete();
        }

        public override void OnExit(MethodExecutionArgs args)
        {
            var transactionScope = (TransactionScope)args.MethodExecutionTag;
            transactionScope.Dispose();
        }
    }
}

Tony THONG · Answer 2 · 2016-12-28T06:43:15.903

2

You can do it using NConcern .NET AOP Framework.

This is an open source runtime AOP framework on which I actively work.

public class DataAccessLayer : IAspect
{
    public IEnumerable<IAdvice> Advise(MethodInfo method)
    {
        //define how to rewrite method
        yield return Advice.Basic.Arround(invoke =>
        {
            using (var transaction = new TransactionScope(...))
            {
                invoke(); //invoke original code
                transaction.Complete();
            }
        });
    }
}

Your business

public class MyBusiness
{
    [Transaction]
    void MyDbMethod()
    {
    }
}

Attach transaction scope aspect to you business

Aspect.Weave<DataAccessLayer>(method => method.IsDefined(typeof(TransactionAttribute), true);

edited Dec 28 '16 at 06:43

answered Nov 24 '16 at 03:59

Tony THONG

772
5
11

Didn't know about this project, seems like quite a nice "starter" alternative to postsharp and fody. The page mentions that it performs the weaving at runtime; how does this affect the performance versus compile-time weaving or fiddling with the binaries with Cecil? – easuter Dec 12 '16 at 09:26
1

Performance is mainly altered in "fire time" not in nominal time. In my own benchmark, it can be faster than PostSharp in nominal use. – Tony THONG Dec 12 '16 at 09:29
Good to hear; I've sort of been looking for something just like this since Postsharp is prohibitively expensive and Fody's extensions are of very inconsistent quality. Thanks for taking the time to post here! :) – easuter Dec 12 '16 at 09:32
1

You're welcome, don't hesitate to give me a feedback to improve the Framework if needed or simply if something is not clear... like I said, i stay really active on this projet. – Tony THONG Dec 12 '16 at 09:39

How to create an aspect decorator to handle EF transactions

2 Answers2