Vic, I will be glad to submit the changes to the project on sourceforge. We have made several extensions to the original BaseDAO design, which we got from you back in 12/01 at the training class. I will need to retrofit the changes I have made to the BaseDAO here into the one in the webPIM project and test them. Once complete, I will submit the change for inclusion in the basejDAO project.
Regards, Todd -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Vic C. Sent: Tuesday, June 11, 2002 3:52 PM To: [EMAIL PROTECTED] Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: Re: [MVC-Programmers] BaseDAO and Update Todd G. Nist wrote: > Hello all, > > I have a question with regards to the update method of the BaseDAO class > found in the WebPIM application. As it is currently written it would appear > to allow for writes of dirty data. That is to say that if two users read > the same record, lets say company record, and user1 changes the company > field to "XYZ" and User2 changes it to "AAAAA", if user2 commits his record > and then user1 commits his, user2's changes will be lost. No exception is > thrown since the update just does an update where the id is equal to the > value of the id of the crs.getBigDecimal("id") of the current row. > > Am I missing something here or is this an issue/bug with the current > implementation? If the update was being applied to the CRS and then the > crs.acceptChanges() method applied, the CRS would handle comparing the > contents of the CRS to the actual db prior to committing the changes, but > since a new connection is obtained and a standard update applied, there is > no support for concurrency. It seems that there either needs to be a > version field on all tables which is included in the update statement of the > prepareUpdateSQL method which does something like below: > > UPDATE theTable SET version=<newversion> [and other fields] WHERE > [criteria] AND VERSION=<oldversion> > > where <oldversion> is the version is the version from the crs current row, > and > <newversion>=<oldversion>+1. > > > In this way if two users update the same record of a table at roughly the > same time, the first ones changes will be committed, but the second ones > will generate an error which can be caught and the end user notified of for > corrective action. > > Any thoughts on this? You are correct! It should check fields and it will. > > I have modified the BaseDAO to support multiple tables rather then one as it > currently does. This opens up another issue of transactional integrity. If > a crs is created from a join between two or more tables, one needs to start > a transaction to support the individual updates as one unit of work. I > have added methods to support transactions to ensure that if the crs has > data from more then one table that either all changes are committed or none > are. > > Any thoughts on this? > You are correct! (alternative is a bean that contains a bean that each have DAO) If you would like to contribute source to the DAO with several other developers, I have added it to sourceforge under basejDAO. I will post the initial code. Just add yourself to the developers list. > Regards, > > Todd G. 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