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HELP: Database server, multiple users, ORM -> me confused

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Message        Markus Winter          Post subject: HELP: Database server, 
multiple users, ORM -> me confusedPosted: Thu Nov 08, 2012 1:17 pm              
           
Joined: Sun Feb 19, 2006 4:00 pm
Posts: 1217
Location: Heidelberg, Germany                Hi all,

I'm not quite sure how one would deal with this:

Let's assume a remote database. Multiple users connect. The information is 
transferred to the users computer for processing (takes a few seconds max). 
Processing is very computer-intensive (searches can't be done by the database - 
we are talking thousands of DNA sequence alignments per user here).

When a record is being opened for editing then the record is being temporarily 
locked in the database. So far so good.

But what if user1 opens the database and receives the records, user2 does the 
same, user1 edits a record and saves the changes ... now user2 is working with 
outdated info. Worse, if user2 edits the same record he overwrites user1's 
changes.

I can imagine that a time-stamp on each record would solve the over-writing 
problem (the record in the database has a newer modification date than the one 
on user2's computer), but how would one ensure that the data on all computers 
are up-to-date?

Thanks for any ideas.

Markus

P.S. About the ORM: I had a look at Bob's ActiveRecord classes and like them - 
but there I run into exactly these problems as well. Are ORMs only for single 
user databases? How do they solve this conundrum?      
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