Hello *, first of all: Sorry for the empty mail to the list: My e-mail client accidentally sent it in HTML format (even though it didn't have any formatting) and the mailing list service seems to cut HTML content away.
Well, I've some code where it is essential that objects read from the datastore are not manipulated by another transaction before they are modified and written to the datastore. In SQL, you use "SELECT ... FOR UPDATE" for this purpose, which locks the records included in the query result just like a write operation does. Using DataNucleus, I searched on http://www.datanucleus.org for how to do this in JDO and it seems to me JDO is lacking this feature. Is that correct? Here's what I found: 1) The page RDBMS persistence properties<http://www.datanucleus.org/products/accessplatform/rdbms/persistence_properties.html> describes the property "datanucleus.rdbms.useUpdateLock" which applies to all queries. This would leave our code pure-JDO (not DataNucleus-dependent), but it's unfortunately not what we need: Most of the time a lock is not required and this option would therefore unnecessarily slow down our application. 2) The page JDOQL<http://www.datanucleus.org/products/accessplatform/rdbms/jdoql.html> shows this code snippet: ((org.datanucleus.jdo.JDOTransaction)pm.currentTransaction()).setOption( "transaction.serializeReadObjects", "true" ); This applies to one transaction and might be very useful, but due to the cast it would make our code highly dependent on DataNucleus. 3) Additionally, the same page mentions that you can set "datanucleus.rdbms.query.useUpdateLock" as a JDOQL extension. I assume that's simply code like this: query.addExtension("datanucleus.rdbms.query.useUpdateLock", "true"); Is it planned for the next JDO version to add update-lock-functionality? IMHO, that's an important feature and should be added to the standard. Best regards, Marco :-) -- *** http://www.jfire.org ***
