Thank you for responding Martin.
As I know, postLoad() is executed in while exporting and while importing as well.
I want to give value to virtual fields through x++ only while exporting.
Therefore, I decided to use mapDataSourceToEntity(). I added it in my extension class.
The code which was in postLoad() and which was working, did not work there.
Therefore, I set a break point exactly on the line of "COC's next" and started debugging.
The debugger was not even popped.
Then I tried the equivalent event handler, copied directly from the entity event list and I had same scenario.
I think I am missing something but I could not figure out what exactly.
Kind regards
