[{"content":"message content","Sender":{"_id":"84d9b802-0ca7-4c49-9391-53b9ddb958bb"},"Receiver":{"_id":"69ac369a-9c34-4dac-ac42-3e12e3821ea4"}},{"content":"message content 2","Sender":{"_id":"69ac369a-9c34-4dac-ac42-3e12e3821ea4"},"Receiver":{"_id":"84d9b802-0ca7-4c49-9391-53b9ddb958bb"}},{"content":"message content 3","Sender":{"_id":"69ac369a-9c34-4dac-ac42-3e12e3821ea5"},"Receiver":{"_id":"84d9b802-0ca7-4c49-9391-53b9ddb958bc"}},{"indexes":[{"name":"myIndex","key":{"Sender._id":1}},{"name":"myIndex2","key":{"Receiver._id":1}}]}]

db.collection.find({$or:[{"Sender._id":"84d9b802-0ca7-4c49-9391-53b9ddb958bb"},{"Receiver._id":"84d9b802-0ca7-4c49-9391-53b9ddb958bb"},]}).explain()