How to keep track of revisions?

Question

I am trying to design my database and I want to have the ability to keep a track of history of changes.

I will have a table that will have all the nutritional facts of an food. When a user makes changes to the item(say changes calories from 100 to 200). I want to make that as a new revision.

That way a person who comes along can see that it was original 100 calories and then was updated to 200 calories. I guess this would be alot like how stack does it now where you can see what has been edited.

I am wondering what is the best way to do this? I am using sql server and nhibernate.

I was thinking of have another column or something that would be revision number. Then every-time a revision is made the number is incremented. Is this a good way?

Answer 1

NHibernate.Envers helps you with that.

Answer 2

You could just do as you've written, add another revision number.

Another approach would be adding a timestamp and use that as history. Every time an item is updated you add a row with the current values and the current timestamp.

Answer 3

I'd normally use some form of audit table(s) to handle this. What we do where I currently work is have all our audit tables under an audit schema, and we have an audit table for every that we wish to track revisions for. We don't use NHibernate, so we simply utilise triggers to ensure that every update to a given row is recorded in the audit table along with a timestamp and user id so you can get some context and order to the way in which the revisions were made.

It seems like it is difficult using triggers with NHibernate, but you could use something like NHibernate interceptors or events as mentioned in this post. I'd say triggers would be preferable to relying on your code, but if this is the only way to go with NHibernate, then maybe it is worth a look.

Lastly, I've seen it mentioned that you can use SQL Servers native audit or trace capabilities. I've never used this myself, but do remember some post on SO suggesting that this replaced the need for creating your own manual audit tables and associated triggers. It seems to do what you want as illustrated by this quote from the link above;

The auditing of activity of users, roles, or groups on database objects can be restricted down to the table level. That is, you can target SQL Server Audit to track specific activities of a user or users down to the individual table level. For example, SQL Server Audit allows a record to be made of all the UPDATEs to the Payroll table by DBO.

To me that sounds more like a true audit rather than just a revision history, but maybe someone with more experience in this area could comment on its feasibility to be used for revision tracking. Of course, you'd have to see what effect it had on NHibernate also.