Creating data of Association Sets.

Hi,

I'm looking for a way to use Create method for a AssociationSet. Example: To create a PO with line items, I will need to pass line item data and header data and then pass this to BAPI_PO_CREATE

Now I need to implement a Gateway service that can create new PO by passing XML payload.

I searched for this but mostly all posts are related to retrieving data of a association by implementing method in the DPC_EXT class but I could not find one to create new one.

Thanks for your help in advance.