make codeigniter automatically insert/update created field and modified field like cake

[eluser]runrun[/eluser]
OK I think I go with both way. Because the mysql solution only insert and update the modified field. I need to insert the datetime to created field as well.

So I make a model to check for created field (if exist), then insert the date. And I want to run this model automatically. But the problem is, technically, the model doesn't know what table to perform with.