Plug-in on pre-validation
Recently we had a requirement to delete the Account record without deleting the associated Contact records.
If we try deleting the account record we’d get the following message box
The relationship definition can’t be updated as well to achieve this
So, we wrote a plugin on the pre-validation stage of pre-delete event of Account, which will retrieve and loop through all the child contact records and set its parent customer field as null.
In case of pre-operation the child records were not available.
Another practical scenario
Hope it helps..