It's also worth noting that an ignored device counts as being something in the folder, so you can always check that by doing:
# dbc 'select * from ap where ap_folder_id=(id that appears in folder view URL)
Example:
URL=demo.airwave.com/ap_list?ap_folder_id=1
# dbc 'select * from ap where ap_folder_id=1'
Can further be simplified to:
# dbc 'select id, name, state from ap where ap_folder_id=1'
This filters out the extra rows that don't matter if you're planning to delete the folder
Database AP States:
0 = pending
1 = approved
3 = ignored