[CONF] Apache Tuscany: RDB DAS CPP - PartialUpdate (page edited)

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RDB DAS CPP - PartialUpdate (TUSCANY) edited by Adriano Crestani
      Page: http://cwiki.apache.org/confluence/display/TUSCANY/RDB+DAS+CPP+-+PartialUpdate
   Changes: http://cwiki.apache.org/confluence/pages/diffpagesbyversion.action?pageId=69449&originalVersion=1&revisedVersion=2






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h1. PartialUpdate

The RDB DAS uses the SDO Change Summary to generate a set of database write operations. Rather than generated a statement to update all columns in a table that maps to a SDO DataObject Type, the DAS generates statements that update ony those columns that map to a modified DataObject property. For example, consider a Customer DataObject that has had the LastName property changed. The *partial update* statement generated by the DAS will look something like this:
{noformat}
UPDATE CUSTOMER SET LASTNAME = 'Tuscany' WHERE ID = '1'
{noformat}
Rather than a statement that updates all columns like this:
{noformat}
UPDATE CUSTOMER SET FIRSTNAME = 'APACHE', SET LASTNAME = 'TUSCANY', SET ADDRESS = 'USA', SET PHONE = '555-5555', SET AGE = '7', SET SHOESIZE = '15' WHERE ID = '1'
{noformat}
There are a couple of very good reasons for using a partial update approach. For one, a performance boost can be realized by applications writing to wide tables. For example, tables with over 100 columns are not unheard of. It can be a huge waste of resource to update 100 columns when only one was modified. Another reason for partial update is that some databases employ [triggers|http://en.wikipedia.org/wiki/Database_trigger]on specific columns in a table. Partial updates are necessary when column triggers are employed to avoid tripping the trigger on every row update rather than only on updates to the specific column. 

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