Built in function may not have been the correct terminology, but basically instead of manually setting the properties you create a relationship object and use the functions to add it to the parent item. (this is my understanding of how this works and I could very well be incorrect)
directly setting:
parentItem.setProperty(“id”,this.getProperty(“source_id”,””) );
this.setProperty(“related_id”, childItem.getID());
I create the relationship object and invoke setRelatedItem & addRelationship, this way if any other housekeeping happens I am covered (I assume).
docRelationship.setRelatedItem(cadDocument); // here is the linkage to the related item
part.addRelationship(docRelationship); // here is the parent (source?) item
