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db.collention.deleteMany()
// db.collection.remove() id deprecated.
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mongo --quiet --eval 'db.getMongo().getDBNames().forEach(function(i){db.getSiblingDB(i).dropDatabase()})'
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# To remove all documents in a collection, call the remove method with an empty query
# document {}. The following operation deletes all documents from the bios collection:
db.bios.remove( { } )