I have two custom objects. Reservation__c and MoneyReceived__c and they are lookup relationship.
I want Reservation__c.totalReceived__c = sum of all MoneyReceived__c.amountReceived__c.
There are one or more amountReceived__c per reservation.
I need help with writing formula calculating
sum of (amountReceived__c) = totalReceived__c
Or do I have to write a class?
For rolling up lookup objects, you will have to write custom code.
You can also levarage Declarative Rollup Summary Tool
You can also refer this blog for step by step instructions
In case you want to write custom code, you can refer this link, which uses a trigger to rollup.
@Logan H since the relationship is lookup relationship you need to write custom code(apex trigger) which you can easily find on internet.
