Workaround for using Roll-up Summary Fields in formula fields
Workaround 1:
1. Create a new field with datatype equivalent to Rollup Summary field's Return type (e.g., Number field if the Rollup Summary returns a Number).
2. Set up a workflow on Rollup Update. Whenever the Rollup field value changes, update the new field (Rollup substitute field) with the Rollup Summary Field value.
3. You can create a Formula expression with a substitute field.
Pros:
Even if the formula expression includes non-Rollup fields, the formula recalculates whenever those fields are updated.
Cons:
Requires creating an additional substitute field for every Rollup Summary field.
Workaround 2:
1. Instead of using a formula field, create a new field (datatype based on the final expression result) in the layout to store the computed expression value.
2. Configure a workflow on Rollup Update to invoke a Deluge function. The Deluge function will compute the expression and update the result to new field.
Pros:
Only one new field is needed to store the final expression value.
Cons:
If the expression involves non-Rollup fields, you have to create another Workflows for Record Create and Record Edit actions and invoke this function.