Before trigger does allows record to be saved when doing validation

Question

I have a before trigger that does some validation and throws an error when any of the criteria is true, but I am seeing that it is only working as an after update which should never be. Why is that?

trigger OpportunityValidationonClosed_Won on Opportunity (before update) {

    List<OpportunityLineItem>opplist=[
        SELECT
            Product2Id, Product2.Name, 
            Opportunity.stagename, OpportunityId, Opportunity.pricebook2Id 
        FROM OpportunityLineItem 
        WHERE Opportunityid IN :Trigger.newMap.keyset() 
        AND pricebookentry.isactive = false 
        AND opportunity.stagename = 'Closed/Won' 
        AND Incremental_AOV__c > 0
        AND Incremental_AOV__c <> null
    ];

    for(OpportunityLineItem oppline : opplist)
    {
        for(Opportunity opp : trigger.new)
        {
            if(!opplist.isempty() || opplist.size() > 0)
            {

                if(opp.pricebook2Id == oppline.opportunity.pricebook2Id && opp.id ==oppline.opportunityid)
                {
                    opp.stagename.addError('LineItem'+ ' '+ '(' + oppline.product2.name + ')'+ ' ' + 'is not an active product for pricebook. Hit Cancel and remove the line item.');
                }
            }
        }
    }
}

Answer 1

I reworked the trigger for you, let me know if it works.......

If it does not add some debug lines in the trigger to test for values to see if they are as expected and get back with us

Also, inspect the debug log and ensure that the query for the oLI is actually returning data. You have a lot of conditions and maybe they are not being met....

trigger OpportunityValidationonClosed_Won on Opportunity (before update) {

    Map<ID,List<OpportunityLineItem>> opplist= New Map<ID,OpportunityLineItem[]>()

    for( OpportunityLineItem oli : [
                                    SELECT
                                        Product2Id, Product2.Name, 
                                        Opportunity.stagename, OpportunityId, Opportunity.pricebook2Id 
                                    FROM OpportunityLineItem 
                                    WHERE Opportunityid IN :Trigger.newMap.keyset() 
                                    AND pricebookentry.isactive = false 
                                    AND opportunity.stagename = 'Closed/Won' 
                                    AND Incremental_AOV__c > 0
                                    AND Incremental_AOV__c <> null
                                ]){

        if(!oppList.containsKey(oli.OpportunityID)){
            oppList.put(oli.OpportunityID,New OpportunityLineItem[]{oli});
        }else{
            oppList.get(oli.OpportunityID).add(oli);
        }
    }


        for(Opportunity opp : trigger.new)
        {
            if(oppList.containsKey(opp.id)
            {
                for(OpportunityLineItem oppLine : oppList.get(opp.id)){
                    opp.stagename.addError('LineItem'+ ' '+ '(' + oppline.product2.name + ')'+ ' ' + 'is not an active product for pricebook. Hit Cancel and remove the line item.');
                }
            }
        }
    }
}