Salesforce的sharing Rule 不支持Lookup型字段解决方案

trigger NOV_Clm_Presentation_Before_InsertUpdate on Clm_Presentation_vod__c(before insert, before update){
            set<Id> productIdSet=new set<Id>();
            system.debug(‘-----------------------‘+productIdSet);
            for(Clm_Presentation_vod__c presentation:trigger.new){
                    if(presentation.Product_vod__c!=null){
                            productIdSet.add(presentation.Product_vod__c);
                            system.debug(‘-----------------------‘+productIdSet);
                    }
            }
            map<id,Product_vod__c> productMap=new map<id,Product_vod__c>([select id,External_ID_vod__c
                                                                          from Product_vod__c 
                                                                          where id in:productIdSet
                                                                        ]);
            system.debug(‘-----------------------‘+productMap);
            for(Clm_Presentation_vod__c presentation:trigger.new){
                    if(productMap.containsKey(presentation.Product_vod__c)){
                            presentation.External_ID_vod__c=productMap.get(presentation.Product_vod__c).External_ID_vod__c;
                            system.debug(‘-----------------------‘+presentation.External_ID_vod__c);
                    }
            }
}