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From Apache Wiki <wikidi...@apache.org>
Subject [Ws Wiki] Update of "Tuscany/TuscanyJava/DAS Java Overview/RDBDAS Java User Guide/OCC" by KevinWilliams
Date Thu, 05 Oct 2006 22:55:46 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Ws Wiki" for change notification.

The following page has been changed by KevinWilliams:
http://wiki.apache.org/ws/Tuscany/TuscanyJava/DAS_Java_Overview/RDBDAS_Java_User_Guide/OCC

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- The RDB DAS is intended for use in disconnected scenarios.  When the DAS returns a graph
of SDO !DataObjects as the result of a query, there are no locks held on the  underlying database
and the data is no longer associated with any database connection or transaction.  Though
locks are not held, the DAS does employ a mechanism called [http://en.wikipedia.org/wiki/Optimistic_locking
Optimistic Concurrency Control] to manage concurrency.
+ The RDB DAS is intended for use in disconnected scenarios.  When the DAS returns a graph
of SDO !DataObjects as the result of a query, there are no locks held on the  underlying database
and the data is no longer associated with any database connection or transaction.  Though
locks are not held, the DAS does employ a mechanism called [http://en.wikipedia.org/wiki/Optimistic_locking
Optimistic Concurrency Control] (OCC) to manage concurrency.
  
+ Basically, when OCC is being utilized, the DAS checks whether the state of the database
has changed since the original data was read before applying any writes to the same location.
 For example, suppose that a DAS client reads a set of Customers, modifys one and then attempts
to write the change back to the database:
+ 
+ {{{
+    Command select = das.createCommand("Select * from CUSTOMER where LASTNAME = 'Williams'");
+    DataObject root = select.executeQuery();
+ 
+    DataObject customer = (DataObject) root.get("CUSTOMER[1]");
+    customer.set("LASTNAME", "Pavick");
+ 
+    //Some period of time passes in which "CUSTOMER[1]" could be modified by another process
or application
+ 
+    das.applyChanges(root);
+ }}}
+ 
+ If OCC is enabled then as part of "applyChanges" processing the DAS will ensure that the
table row representing "CUSTOMER[1]" has not been changed since it was read.
+ 

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