Why do DAOs have separate create and update methods?

I'm looking at a couple of designs for DAO interfaces. One has a single update() method, whi开发者_运维技巧le the other has separate create() and update() methods.

Assuming that it's possible to do something along the lines of 'insert otherwise update', what's the benefit of a separate create() method? Is there something to do with concurrency lurking there?

Thanks in advance for your help.

Cheers, Ross

I use two seperate methods when creating DAO's simply for Clarity and Explicitness.

If there is a single Update method and somebody passes in an existing object, it will be updated. But what if the person really wanted to Create a new object and the fact that it already existed is an error?

With a single Update method, there's really no way for anybody to tell what EXACTLY is going on behind the scenes.