db={"houses":[{"_id":"601bae8e26ed00591d571dbe","name":"Facebook testing department","district":"Los-Angeles","locality":"Facebook","events":["601bae8e26ed00591d571dbf"]},{"_id":"601bae8e26ed00591d571dbc","name":"Facebook office","district":"Los-Angeles","locality":"Facebook","events":["601bae8e26ed00591d571dbd"]}],"events":[{"_id":"601bae8e26ed00591d571dbf","event":"Testing","details":"Testing software for production","date":"2020-07-31T21:00:00.000Z"},{"_id":"601bae8e26ed00591d571dbd","event":"Conference","details":"Developers conference about 12345","date":"2020-07-31T21:00:00.000Z"}]}

db.houses.aggregate([{$match:{locality:"Facebook"}},{$lookup:{from:"events",let:{events:"$events"},pipeline:[{$match:{$and:[{$expr:{$in:["$_id","$$events"]}},{event:"Conference"}]}}],as:"events"}},{$match:{events:{$ne:[]}}}])