Thank you, Kevin, for your idea. I wanted to do the same thing, and your idea worked wonderfully because of the transaction stuff that Mike explained. I noticed, however, that using REQUEST.set, then passing REQUEST to manage_changeProperties has a very nasty side effect: All of the properties of the object may be changed, not just newid. For example, if REQUEST happens to contain {"title": "new title"}, then your folder gets its title changed. This is what I ended up doing: folder id="repository" property next_id = 1 property id_template = "doc-%06d" dtml-method "get_new_id" = <dtml-let id=next_id> <dtml-call "manage_changeProperties({'next_id': id + 1})"> <dtml-return "id_template % id"> </dtml-let> Then I just call get_new_id whenever I want to get a unique id for a new item in the repository folder. -----Original Message----- From: Michel Pelletier [mailto:michel@digicool.com] Sent: Saturday, September 11, 1999 10:09 AM To: Kevin Dangoor Cc: zope@zope.org Subject: Re: [Zope] Unique incrementing IDs Kevin Dangoor wrote:
Hi,
Since Zope is multithreaded, it seems like there could be a problem doing something like this:
<dtml-comment newid is a folder property> <dtml-call "REQUEST.set('newid', newid + 1)"> <dtml-call "manage_changeProperties(REQUEST)"> <dtml-call "REQUEST.set('id', newid)"> <dtml-with "manage_addProduct['SomeProduct']"> <dtml-call "ZClass_add(_.None, _)"> </dtml-with>
It seems plausible that you might end up trying to create two objects with the same ID. This will obviously fail, but it would be nice if there was
an
easy way to get the next ID sequentially like this. Am I correct in assuming that there may be a condition where it tries to create two objects with the same ID?
Yes. This would cause the database to raise a 'ConflictError'. If this happes, one thread wins and one thread looses. The looser's transaction is completely aborted, and the loosers request is resubmitted in a whole new transaction. This works well to avoid the problem your thinking about. -Michel