Create Validation for a custom object line item on an opportunity

Question

I have created a custom object called Billing Forecast with a master-detail relationship to the opportunity object. When an opportunity is closed won I need to ensure that the user enters at least one billing forecast.

A billing forecast consists of a currency field for each month of a year. Each year then becomes a billing forecast. I have tried a couple of different formulas but no luck.

Answer 1

You can just create a rollup summary field on the opportunity object that is the count of Billing Forecast objects. Then you can use a validation rule that checks that the rollup summary field is greater than 0. Something like this

AND(
     ISCHANGED(StageName),
     TEXT(StageName) = "Closed Won",
     Rollup_Summary_Field__c < 1
)

Just need to make sure you put in your own field API Names