Question: I need to implement an audit trail for Add/Edit/Delete on my objects,I'm using an ORM (XPO) for defining my objects etc. I implemented an audit trail object that is triggered on 

1. OnSaving
2. OnDeleting

Of the base object, and I store the changes in Audit-AuditTrail (Mast-Det) table, for field changes. etc. using some method services called.

How do you implement audit trail in you OOP code? Please share your insights? Any patterns etc? Best practices etc? Another thing is that how to disable audit when running unit test,since I don't need to audit them but since base object has the code.

Changes to object (edit/add/del) and what field changes need to be audited

Answer: 
I don't know if it will fit seamlessly with your ORM, but i used [Point-in-Time](http://www.simple-talk.com/sql/database-administration/database-design-a-point-in-time-architecture/) database design for an ERP application and really recommend it. You automatically get History and Audit from this architecture, as well as other benefits.
We've implemented a similar solution, using AOP (aspectJ implementation). Using this particular points can be captured and specific operations can be performed.

This can be plugged in and plugged off when we like.

If you really want to do it in the app layer, i would suggest this.

Hope it helps..