Way for Adding Total Oppty Line Item to Opportunity Field

Question

How can I combine both the total oppty line items (Total__c) (roll-up field in opportunity) and Miscellaneous_Fee__c (currency field in opportunity) in just one field using apex trigger? This miscellaneous fee is per opportunity, not per line item.

For practice, I used both the Opportunity and Opportunity Line Item objects. Here are some fields from these two:

Opportunity: Name, Date__c, Miscellaneous_Fee__c, Total__c

Opportunity Line Item: Product_Name__c, Price__c

Answer 1

A good way for doing that is to keep both fields (you don't have to put them on the layout) and use a formula field that displays (Total__c + Miscellaneous_Fee__c).

If you want a trigger, you need to check if the Miscellaneous_Fee__c has been changed and them put the sum on another field:

for(Opportunity opp : Trigger.new){
    if(opp.Miscellaneous_Fee__c != Trigger.OldMap.get(opp.Id).Miscellaneous_Fee__c){
        opp.Total_Sum_Field__c = opp.Miscellaneous_Fee__c + opp.Totals__c;
    }
}

You can also use a workflow for that.

Answer 2

First of All, If Opportunity line items exists under an Opportunity then the Opportunity Amount is the summation of Opportunity Line Item Pricing values.

So, you do not need to write any trigger for calculation, or no need to create separate roll up summary field for calculation.

Workaround no.1

Make Total__c as Formula (Currency) field and calculate as follows:

Total__c = Amount + Miscellaneous_Fee__c

Workaround no.2

Make Total__c as Currency field and update that by workflow field update with the above calculation.