Database
[{dirId:"1",dirName:"firstDir",usersRead:["user1","user2"],userWrite:["user2","user3"]}]
Query
db.collection.aggregate([{"$addFields":{"allUsers":{$setUnion:["$usersRead","$userWrite"]}}},{"$unwind":"$allUsers"},{"$project":{dirId:1,dirName:1,userId:"$allUsers",canRead:{"$cond":{"if":{"$in":["$allUsers","$usersRead"]},"then":"Y","else":"N"}},canWrite:{"$cond":{"if":{"$in":["$allUsers","$userWrite"]},"then":"Y","else":"N"}}}}])