db={"col1":[{"_id":ObjectId("5ec293782bc00b43b463b67c"),"status":["running"],"name":"name1 ","dcode":"dc001","address":"address1","city":"city1"},{"_id":ObjectId("5ec293782bc00b43b463b671"),"status":["running"],"name":"name2","dcode":"dc002","address":"address2","city":"city2"}],"col2":[{"_id":ObjectId("5ec296182bc00b43b463b68f"),"scode":ObjectId("5ec2933df6079743c0a2a1f8"),"ycode":ObjectId("5ec293782bc00b43b463b67c"),"city":"city1","lockedDate":ISODate("2020-05-20T00:00:00Z"),},{"_id":ObjectId("5ec296182bc00b43b463688b"),"scode":ObjectId("5ec2933df6079743c0a2a1ff"),"ycode":ObjectId("5ec293782bc00b43b463b67c"),"city":"city1","lockedDate":ISODate("2020-05-20T00:00:00Z"),},{"_id":ObjectId("5ec296182bc00b43b44fc6cb"),"scode":null,"ycode":ObjectId("5ec293782bc00b43b463b67c"),"city":"city1","lockedDate":ISODate("2020-05-20T00:00:00Z"),},{"_id":ObjectId("5ec296182bc00b43b44fc622"),"scode":"","ycode":ObjectId("5ec293782bc00b43b463b67c"),"city":"city2","lockedDate":ISODate("2020-05-20T00:00:00Z"),}]}

db.col1.aggregate([{"$match":{city:"city1"}},{$lookup:{from:"col2",let:{id:"$_id",city:"$city"},pipeline:[{$match:{scode:{"$ne":null},lockedDate:ISODate("2020-05-20T00:00:00Z"),$expr:{$and:[{$eq:["$ycode","$$id"]},{$eq:["$city","$$city"]}]}}},{$project:{_id:1}}],as:"col2"}},{$project:{_id:0,name:1,countOfCol2:{$size:"$col2"}}}])