StockItemDuplicateTriggerRd2

if(Trigger.isInsert && Trigger.isBefore) {
		//call the class in your handler for before insert
		// StockItemHandler.onBeforeInsert(Trigger.new);
       
       //We create a set to accept all the incoming records. Sets don't allow duplicates, 
        //so this is good for bulk uploads--imagine somemone uploading a CSV of 1000 pot holders. 
        //We only want the record once!
        Set<String> stockItemSet = new Set<String>();
        //Starting a for loop to inspect the records coming into the trigger.
        for(Stock_Item__c si : Trigger.new){
            //Adding the Stock Item Name to the set. This is what we are deduping on. 
            stockItemSet.add(si.Item_Name__c);        
 	    } 
        

        //Created a new list where we are looking at all our existing stock items and only grabbing those
        //where the Item Name matches the Item Name in our above set.
        List<Stock_Item__c> stockItemList = New List<Stock_Item__c>([SELECT Id, Item_Name__c 
                                                                    FROM Stock_Item__c 
                                                                    WHERE Item_Name__c
                                                                    in: stockItemSet]);
        
        //So now we're creating a Map. In theory, we could have used another Set since 
        //we are comparing on one value but a Map allows you to access all 
        //other related information on the record which could be useful.
        //
        //Key goes first (in this case, Stock Item Name) then value (Stock Item record). 
        //Remember, you can have ONE unique key, but many values. 
      
        Map<String, Stock_Item__c> stockItemMap = New Map<String, Stock_Item__c>();
        //Okay, entering another loop where we are talking about all the items that were in our list above.
        //We are going to iterate over all the records in the list.
        for(Stock_Item__c si: stockItemList){
        //Using the .put method, we are putting the Stock Item Name and Stock Item record into our set.
        //When we exit the loop, we'll have a bunch of Stock Items and their names linked together 
        //(remember: key/value pair!)
         stockItemMap.put(si.Item_Name__c, si);
        } 
        //Another loop! Notice we are back to Trigger.new this is because we need to assess all the records
        //that have been created in Trigger
        for(Stock_Item__c si : Trigger.new) {  
        if(stockItemMap.containsKey(si.Item_Name__c))  
        //si.Item_Name__c = 'DUPLICATE ' + si.Item_Name__c;  
        si.addError('Looks like you\'re trying to add a dupe record!');
        }   
       
    }