db={"users":[{"_id":ObjectId("62093266db5c0830fe3397ea"),"email":"naved@gmail.com","role":"owner","systemID":["12345678","20200302","33512445"],"mobile":"9876543210"}],"systemIds":[{"_id":ObjectId("6212d42aab85a3b9f7559e02"),"bPID":"12345678",/** primary key*/"bPVoltage":45.9,"capacity":"5","alerts":["201","342"],"state":2,"stateOfCharge":98},{"_id":ObjectId("6212d42bab8ba3d9f7599ea2"),"bPID":"20200302","bPVoltage":45.9,"capacity":"2","alerts":["200"],"state":0,"stateOfCharge":48},{"_id":ObjectId("6212d42aab85a3b9f7559e01"),"bPID":"20200302","bPVoltage":45.9,"capacity":"5","alerts":["315"],"state":1,"stateOfCharge":78},{"_id":ObjectId("6212d42aab85a3b9f7559e24"),"bPID":"33512445","bPVoltage":45.9,"capacity":"19","alerts":["31533"],"state":1,"stateOfCharge":73}]}

db.users.aggregate([{$match:{"_id":ObjectId("62093266db5c0830fe3397ea")}},{$project:{systemIDs:{$filter:{input:"$systemID",as:"item",cond:{$regexMatch:{input:"$$item",regex:"12"}}}}}},{$unwind:"$systemIDs"},{$lookup:{from:"systemIds",localField:"systemIDs",foreignField:"bPID",as:"systemIds"}},{$sort:{systemIDs:1}},{$skip:0},{$limit:1}])