Restrict Duplicate Products in Opportunity

Hello Salesforce Developer,

I am sharing trigger code to avoid duplicate products on a particular opportunity.

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trigger RestrictDuplicateProducts on OpportunityLineItem (before insert) { Map<id, Set<Id>> mapOpportunityProducts = new Map<id, Set<Id>>(); Set<Id> oppIdSet = new Set<Id>(); Set<Id> oppLineItemToSkip = new Set<Id>();// skip these items from query for (OpportunityLineItem oppLineItem: Trigger.new) { if(!String.isblank(oppLineItem.id)){ oppLineItemToSkip.add(oppLineItem.id); } oppIdSet.add(oppLineItem.OpportunityId); } system.debug('find me=>'+oppLineItemToSkip); // query all existing line items to check duplicate products List<Opportunity> opps = [Select id, (Select id,Product2Id FROM OpportunityLineItems WHERE id not in : oppLineItemToSkip) FROM Opportunity WHERE Id in : oppIdSet]; for(Opportunity opp : opps){ Set<Id> productIdSet = new Set<Id>(); for(OpportunityLineItem oppLineItem : opp.OpportunityLineItems){ productIdSet.add(oppLineItem.Product2Id); } mapOpportunityProducts.put(opp.Id,productIdSet); } for (OpportunityLineItem oppLineItem: Trigger.new) { if( mapOpportunityProducts.containsKey(oppLineItem.OpportunityId) ) { if(mapOpportunityProducts.get(oppLineItem.OpportunityId).contains(oppLineItem.Product2Id)){ oppLineItem.addError('An Opportunity Line Item already exists.'); } mapOpportunityproducts.get(oppLineItem.OpportunityId).add(oppLineitem.Product2Id); } else{ mapOpportunityProducts.put(oppLineItem.OpportunityId, new Set<Id>{ oppLineItem.Product2Id }); } } }