Is it possible to do a reverse relation query in a custom entry source?
https://docs.craftcms.com/v2/plugins/hooks-reference.html#modifyentrysources
I have two entry sections, one called courses and one called course occurrences. Course occurrences are linked via an entries field called parentCourse. It easy enough to query course occurrences that don't have a parent course (check if parentCourse is empty/not empty, but the reverse seems to be a little more complex.
I'm looking for the ability to have a custom entry source that lists all the parent course records that don't have a child record basically, making it a reverse relation.
I tested the Reverse Relations plugin and it does display the children entries related on the parent so the relation works, but I was wondering if it can be done directly through a criteria query in the modifyEntrySource hook?
