Database
[{_id:ObjectId("5a934e000102030405000000"),"requests":[ObjectId("5a934e000102030405000001")],followers:[ObjectId("5a934e000102030405000001")]},{_id:ObjectId("5a934e000102030405000001"),"requests":[ObjectId("5a934e000102030405000002")],followers:[ObjectId("5a934e000102030405000001")]},{_id:ObjectId("5a934e000102030405000002"),"requests":[ObjectId("5a934e000102030405000003")],followers:[ObjectId("5a934e000102030405000003")]}]
Query
db.collection.update({},[{$set:{requests:{$filter:{input:"$requests",cond:{$ne:["$$this",ObjectId("5a934e000102030405000001")/** userId*/]}}},followers:{$cond:{if:{$not:{$in:[ObjectId("5a934e000102030405000001"),/** userId*/"$requests"]}},then:{$filter:{input:"$followers",cond:{$ne:["$$this",ObjectId("5a934e000102030405000001")/** userId*/]}}},else:"$followers"}}}}],{multi:true})