Database
[{"_id":ObjectId("5f14081c14c08a261b816d57"),"battery_voltage":3673,"total_usage":0.483,"signal":14,"samplehour":"2020-07-18T23:59:59-04:00","sampledate":"2020-06-18T23:59:59-04:00"}]
Query
db.collection.aggregate({$addFields:{"month":{$month:{$toDate:"$sampledate"}}}},{$match:{month:6}})