Re: Back from the dead with a racing question!

On Fri, Jul 17, 2009 at 1:54 PM, Jason Pruim<jason@jasonpruim.com> wrote: > > On Jul 17, 2009, at 11:56 AM, Bastien Koert wrote: > >> On Fri, Jul 17, 2009 at 11:51 AM, tedd<tedd.sperling@gmail.com> wrote: >>> >>> At 11:12 AM -0400 7/17/09, Jason Pruim wrote: >>>> >>>> Hi everyone! >>>> >>>> So some of you may have noticed that I have been away for quite >>>> awhile... >>>> Been trying to get settled (Moved across the country) and getting a job. >>>> >>>> And now that that is done I have a question about a project that I might >>>> be doing for my current employer and want to do it properly. >>>> >>>> If all goes through, I'll be writing an online database that upwards of >>>> 10 >>>> people will be using at various times through out the day. Basically, in >>>> a >>>> form they fill out a model number, customer name, phone number etc. >>>> etc.. >>>> And then submit the form. After submitting they need to write the log >>>> number >>>> on some paperwork. If I have 2 people submit the form at the same time, >>>> I'm >>>> thinking I could end up with a race condition and they might get the >>>> wrong >>>> log number (The log number is simply a consecutive record number) >>>> >>>> Do I need to be reading up on locking tables/rows? Or in my situation as >>>> I've briefly described it do I not have to worry about it? Or is there a >>>> third door with the magic bullet that will solve all my problems? :) >>>> >>>> Any advice is greatly appreciated as always, RTFMing is good as well, as >>>> long as M is defined :) >>>> >>>> I'm not afraid of google either, just need the right terms to hit it >>>> with >>>> so I don't go into "search overload" as the commercials for a rival >>>> search >>>> engine claim :) >>>> >>>> Thanks Everyone! >>> >>> Jason: >>> >>> Welcome back. >>> >>> Clearly if you have two or more people checkout the same record at the >>> same >>> time and each edits the record then you ARE going to have problems when >>> each >>> updates the record. >>> >>> You can solve this problem by using transactions -- here's a link: >>> >>> >>> http://dev.mysql.com/doc/refman/5.0/en/lock-tables-and-transactions.html >>> >>> When someone is editing a record, you also need to be able to show the >>> next >>> person(s) that the record they want is currently busy and not available.. >>> However, I'm not sure as to how to notify the next user that the table is >>> locked via php. Perhaps a table status might provide that information. If >>> so, then use that to notify the next user. >>> >>> As for your log of activity, just create a another record (with an >>> auto_increment index) in your activity log table and update that record >>> with >>> the data you need to record, such as user id, timestamp, what record they >>> accessed and whatever else you want after the transaction is completed. >>> >>> Cheers, >>> >>> tedd >>> >>> -- >>> ------- >>> http://sperling.com >>>  http://ancientstones.com >>>  http://earthstones.com >>> >>> -- >>> PHP General Mailing List (http://www.php.net/) >>> To unsubscribe, visit: http://www.php.net/unsub.php >>> >>> >> >> As a further note to tedd's reply on transactions, you will need to >> use the INNODB engine in mysql should you want to use transactions. >> Transactions here are done a row locking level not table so you should >> have fewer issues. > > I also just found out that unless I can convince them to host it off site, > it'll be on a windows machine....  So php & mssql... Does that change alot? > > To answer some of the other questions the Log number is currently just an > auto incrementing consuctive number. So an auto+increment would work > perfectly. What I'm trying to avoid is: > > User1 > User2 > > User1 submits to log number 12345 > User2 submits to log number 12346 > > User1 is told their log number is 12346 > User2 is told their log number is 12346 > > But User1 & User2 are on different computers... And if it's as easy as using > the equivelant for: SELECT * FROM table WHERE UserID="User1" ORDER BY > lognumber desc LIMIT 1; Then I'm good... I know how to proceed with writing > it... Just need to figure out how to bill/sell it! ;) > > > > > -- > PHP General Mailing List (http://www.php.net/) > To unsubscribe, visit: http://www.php.net/unsub.php > > MSSQL doesn't allow limit, but you can do a select top 1 * from table [where] [order by lognumber desc] -- Bastien Cat, the other other white meat