NHibernate IInterceptor: an AuditInterceptor

As I was playing around with NHibernate today, I came accross a rather inconvenient problem. :).

Let me first explain what I wanted to achieve:
For every domain object that I save, I want to persist in the database when the entity has been created, when it has been last updated and by whom. Nothing special, just regular audit-information.

To make this all possible, I've created the following classes / interfaces:

• IAuditable interface

  
  
  
  

• AuditableEntity interface

  
  
  

I think this is pretty straightforward and doesn't require any further explanation.
Then, I continued with creating an NHibernate interceptor which would set the Created and Updated dates. (I could also used the ILifecycle interface instead, but this meant that I would have a dependency to the NHibernate assembly in my 'domain classes assembly', and I don't like that. In fact, the ILifecycle interface has been deprecated for exactly that reason).

This is an extract from my AuditInterceptor which would perform the task I wanted (at least, I thought so ... ).
(Note that my AuditInterceptor is NOT in the same assembly where the IAuditable, AuditableEntity and other domain base class reside in. This would create a dependency from my base classes to NHibernate and again, I hate this :) ).

The AuditInterceptor (snippet):


As you can see, it is very simple: I only had to implement 2 methods of the IInterceptor interface:

• OnSave, which is called when an entity is saved for the first time in the database (INSERT)


• OnFlushDirty, which is called when an existing entity is dirty and has to be updated

What I do, is check whether the entity that is to be saved implements the IAuditable interface, and if so, I just set the necessary properties (Created and Updated) to the appropriate values (the current DateTime).

Easy enough, simple, understandable and clean... If only this would work...
During testing, I got the following exception:

  ----> System.Data.SqlTypes.SqlTypeException : SqlDateTime overflow. 
Must be between 1/1/1753 12:00:00 AM and 12/31/9999 11:59:59 PM.
   at NHibernate.Persister.Entity.AbstractEntityPersister.Insert(Object[] fields, 
Boolean[] notNull, SqlCommandInfo sql, Object obj, ISessionImplementor session)

As it turns out, NHibernate doesn't 'see' the changes you make to the entity parameter that is passed to the Interceptor methods:



You can however, change the values that are in the state array parameter. Then NHibernate will correctly persist the changes.

But, I do not like to 'hard-code' property names as strings for obvious reasons (if you change a property, the compiler will not detect that you should change your 'hardcoded property name string', etc...).

Anyway, in order to get my interceptor to work, I have no other choice then messing around with the propertyNames[] and state[] parameters.
In order to get rid of the 'weak-typing', I added a little bit more code.
So, now my classes look like this:

• IAuditable interface

  
  



• AuditableEntity class

  
  



• AuditInterceptor

  
  

This solution is, IMHO, elegant enough to live with, and it works.

However, maybe someone else has a better, more elegant solution for this ? If so, I'd like to hear from you ...