[{"facilityId":1,"file":[1,2,3,4,5]},{"facilityId":2,"file":[1,2,3,]},{"facilityId":3,"file":[1,2,3,4,5,6,7]}]

db.collection.aggregate([{$match:{facilityId:{$in:[1,2]}}},{$project:{facilityId:1,file:{$slice:["$file",4]}}}])