This is not ideal, though, because it means that you can't read the comments either. Fortunately, with Workflow From Case Comments, there is a better way. As I mentioned in my previous blog entry, Workflow From Case Comments is a "chaining" workflow, which means that when it edits the parent case, it kicks off the workflow anew on that case object. We can use this to our advantage in solving this problem. Here's how.
- Define a checkbox-type custom field on Case called "No more comments." Do not add it to any of the Case page layouts.
- Make a validation rule which shows the error "You cannot add comments to a closed case" at the top of the page. In the formula section put simply "No_more_comments__c=true".
- Make a Workflow on the Case Comments object which fires when Case: Closed equals True.
- Make a Field Update in that workflow which sets the No More Comments field to true.
- Activate the workflow rule!
Workflow From Case Comments to the rescue!