Transfer of Custom Fields from ECC PR to SRM SC in ECC EHP6

Dear all,

working in SRM 7.02, ECC 6. using PI the data is transferred to SRM from ECC.

1.I have some custom fields in SRM SC, while transferring the PR from ECC this custom fields should be filled from some standard field in ECC and custom field in ECC.

So i have gone through some documents,

check the badi - /sapsrm/bd_soa_mapping method MAP_BACKEND_TO_XI. But when i check the Badi and try to implement the same.

in the service - PurchaseRequestERPSourcingRequest_In Strucutre of SC -/SAPSRM/PUR_REQ_ERPSRC_REQ inside we have another strucutre - /SAPSRM/PUR_REQ_ERPSRCG_REQ_P1.

These stutcure doesn't have my custom field. How can i write coding to map the standard field coming from xml is mapped to custom field in SC .

Kinldy guide me on this.

thank you..