Friday, September 9, 2011

AoP Transactions Redux

Yesterday I highlighted the issues I was having with "Aspectising" the Unit of Work with regards to concurrency management. After a bit of research I was able to find some resources on the issue that confirmed my suspicions.

I identified that in many cases it was the responsibility of the business logic to determine the actions undertaken in the event of a commit failure (whether it be due to concurrency or some other failure), and that using AoP to wrap the transaction removes any chance for the method itself to perform the appropriate resolution steps.

As it turns out, I am not the only one to come across this issue, as described in this paper This paper described the problem I encountered in a much more scientific manner than I possibly have the time or skill to, but it comes to very much the same conclusions I did. Yes it is possible, but a) does it make sense, and b) the solution would be so complex that it would defeat the purpose of cross-cutting implementation, which is to reduce complexity.

The paper also discusses one of the issues I highlighted in previous posts where a solution I proposed to manually manage a transaction for specific business functions would need to be configured in such a way as to only allow execution if not within an existing transaction scope, and similarly AoP managed transaction methods could not be called from within the manually managed transaction method. This is mentioned in chapter 7 when discussing the EJB transaction policies, which is essentially what I was describing in my discussion.

So… my final recommendation is:

  • Remove the AoP Unit Of Work implementation as step 1.

  • Ensure each business logic method manages its own transaction scope

  • Ensure Public methods perform the transaction/concurrency commits, and do not call other public methods

  • Ensure private methods are always within the scope of a public method transaction, and do not handle concurrency failures (as they will only trigger when the outer transaction commits anyway)

This is a fairly generalised solution and might need a better definition, but it should be possible to adhere to these rules to improve consistency of the application and ensure the behaviour is predictable.

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