Re: Enforcing constraints; Sessions and Threading

[Dan Diephouse]

Jukka Zitting wrote: Hi, On 11/5/07, Dan Diephouse <[EMAIL PROTECTED]> wrote: This is probably a horrendously stupid question, but I'm hoping someone can help me figure out how to enforce constraints nodes. I'm writing a JCR store for Abdera to store Atom entries. I'm creating a node for each entry and one of the properties on the node is the "resource name". (I.e. what's in the HTTP URL - /my_entry.atom). I don't ever want to have multiple nodes with the same resource name property. Whats the best way to enforce this so I can never have two threads create the same resource at the same time? There's nothing like a UNIQUE constraint in JCR or Jackrabbit (though it might be good to have at least a Jackrabbit feature request in Jira for that), so the closest you can get probably to make the "resource name" be the name of the entry node and have all the entries stored as children of a parent node that doesn't allow same-name-siblings. OK that could work! Alternatively you need to implement that constraint in your code. Whenever creating a new node (or modifying the "resource name" property) you could lock the subtree (or just a separate lock node) and check that the constraint isn't being violated before saving the changes. I really don't want to lock the whole collection of entries though. That would mean I would get a LockException if another thread tried writing to that node, which 99.9999% of the time won't cause a conflict. Cheers, - Dan -- Dan Diephouse MuleSource http://mulesource.com | http://netzooid.com/blog