Question

According to REST philosophy, a PUT operation should create an entity if it doesn’t exist, or update it if it does. So for example, if a client does this operation:

PUT http://server/user/5?firstname=John&lastname=Doe

I should expect that a user with an ID of 5 either be created or updated.

The update case is easy with NHibernate; simply retrieve the user and update the firstname and lastname.

However, how do I create a user with an ID of 5? By default, NHibernate manages all entity IDs. Even if you set the ID yourself, NHibernate will ignore it and replace it with its own. If I switch to using assigned IDs, then I can assign a new user with an ID of 5, but then I’d lose a lot of NHibernate’s features.

So in other words, is there a way to configure NHibernate to use a generated ID if one is not provided, and to use the user-set ID if one is provided? If not, how do I get around this problem of PUT creation with NHibernate?

Answer 1

If you do a

PUT http://server/user/5

and the server creates the object but nHibernate changes the id then, return the HTTP status code 301 - Moved permanently and put the new URI in the Location header.

The client should detect the 301 and update any stored URLs with the old Id.

Just a word of warning, PUT semantics are not really Create and Update, they are replace. So if you send a representation that contains just last name and first name, then if you do things by the book, then all other information that was previously stored about that user is lost.