Trigger to update an Opportunity field when a new Opportunity Product is added or edited.

Here's an example of a trigger that can help you accomplish this:
Copy code : 
trigger UpdateOpportunityFields on OpportunityLineItem (after insert, after update) {
    // Map to store OpportunityIds and the sum of Custom_Prod_Field_1__c and Custom_Prod_Field_2__c for each Opportunity
    Map<Id, OpportunityFields> oppFieldsMap = new Map<Id, OpportunityFields>();
    // Iterate through the OpportunityLineItems and store the sum of Custom_Prod_Field_1__c and Custom_Prod_Field_2__c for each Opportunity
    for (OpportunityLineItem oppLineItem : Trigger.new) {
        // Check if the OpportunityId is not already in the map
        if (!oppFieldsMap.containsKey(oppLineItem.OpportunityId)) {
            // Create a new OpportunityFields object and add it to the map
            OpportunityFields oppFields = new OpportunityFields();
            oppFields.OpportunityId = oppLineItem.OpportunityId;
            oppFields.Custom_Opp_Field_1__c = oppLineItem.Custom_Prod_Field_1__c;
            oppFields.Custom_Opp_Field_2__c = oppLineItem.Custom_Prod_Field_2__c;
            oppFieldsMap.put(oppLineItem.OpportunityId, oppFields);
        } else {
            // If the OpportunityId is already in the map, update the sum of Custom_Prod_Field_1__c and Custom_Prod_Field_2__c
            OpportunityFields oppFields = oppFieldsMap.get(oppLineItem.OpportunityId);
            oppFields.Custom_Opp_Field_1__c += oppLineItem.Custom_Prod_Field_1__c;
            oppFields.Custom_Opp_Field_2__c += oppLineItem.Custom_Prod_Field_2__c;
        }
    }
    // Create a list to store the updated Opportunities
    List<Opportunity> oppsToUpdate = new List<Opportunity>();
    // Iterate through the map and update the Opportunity fields
    for (OpportunityFields oppFields : oppFieldsMap.values()) {
        Opportunity opp = new Opportunity();
        opp.Id = oppFields.OpportunityId;
        opp.Custom_Opp_Field_1__c = oppFields.Custom_Opp_Field_1__c;
        opp.Custom_Opp_Field_2__c = oppFields.Custom_Opp_Field_2__c;
        oppsToUpdate.add(opp);
    }
    // Update the Opportunities
    if (!oppsToUpdate.isEmpty()) {
        update oppsToUpdate;
    }
}
// OpportunityFields class to store the OpportunityId and the sum of Custom_Prod_Field_1__c and Custom_Prod_Field_2__c for each Opportunity
public class OpportunityFields {
    public Id OpportunityId { get; set; }
    public decimal Custom_Opp_Field_1__c { get; set; }
    public decimal Custom_Opp_Field_2__c { get; set; }
}
This trigger listens to the `