SC number or SC parent GUID for already ordered/saved SC

Hello experts,

I have a custom logic to place for already ordered/saved SC in web dynpro component /SAPSRM/WDC_DODC_NA view V_DODC_ATTACHMENT in SRM 7.0 landscape.

I have created an post exit for onactionclick_description and custom logic is dependent on SC number based on which I will fetch details from one custom table and proceed.

Is there any way to get shopping cart in this webdynpro post exit to go ahead. Any class/method which gives us SC number for current instance?