[TYPO3-mvc] prevent extbase from updating my records

[Stefan Frömken]

Hello MVC-List,

I have to group some objects and numeric properties have to be summed 
up. But when I execute a setter of my object, this record gets updated 
in my database! How to prevent extbase from updating my database? This 
new value is only for fluid and extbase internally calculations, but 
never for the DB!

Stefan