M101P: MongoDB for Developers - Final Exam

Q1

> db.messages.find({"headers.From":"[e-mail]","headers.To":"[e-mail]"},{"headers":1}).count()3

Q2

# To 存在重复的db.messages.aggregate([{$project:{"headers.From":1,"headers.To":1}},{$unwind:"$headers.To"},{$group:{_id:{id:"$_id",from:"$headers.From",to:"$headers.To"},count:{$sum:1}}},{$match:{count:{$gt:1}}}],{allowDiskUse:true}){ "_id" : { "id" : ObjectId("4f16fc98d1e2d32371004584"), "from" : "[e-mail]", "to" : "[e-mail]" }, "count" : 2 }# 确认db.messages.find({_id:ObjectId("4f16fc98d1e2d32371004584")})    "[e-mail]",    ...    "[e-mail]",# 测试 setUnion 是否能去重#db.messages.aggregate([ {$project:{"headers.From":1,"headers.To":1,newto:{$setUnion:["$headers.To"]}}},{$match:{"$headers.To.1":{$exists:true}}} ])db.messages.aggregate([ {$project:{"headers.From":1,"headers.To":1,newto:{$setUnion:["$headers.To"]}}},{$match:{_id:ObjectId("4f16fc98d1e2d32371004584")}} ]).pretty()# 错误的方法db.messages.aggregate([{$unwind: "$headers.To"}, {$group : {_id : {"from": "$headers.From", "to" : "$headers.To"}, emails : {$sum: 1}}}, {$sort: {emails : -1}}, {$limit: 5}])# 正确的方法db.messages.aggregate([{$project:{"headers.From":1,"headers.To":1,newto:{$setUnion:["$headers.To"]}}},{$unwind:"$newto"},{$group:{  _id:{from:"$headers.From",to:"$newto"}  ,count:{$sum:1}  }},{$sort:{count:-1}},{$limit:5}]){ "_id" : { "from" : "[e-mail]", "to" : "[e-mail]" }, "count" : 750 }{ "_id" : { "from" : "[e-mail]", "to" : "[e-mail]" }, "count" : 679 }{ "_id" : { "from" : "[e-mail]", "to" : "[e-mail]" }, "count" : 646 }{ "_id" : { "from" : "[e-mail]", "to" : "[e-mail]" }, "count" : 616 }{ "_id" : { "from" : "[e-mail]", "to" : "[e-mail]" }, "count" : 567 }# 另一种正确的方法db.messages.aggregate([    {"$unwind" : "$headers.To"},    {        "$group" : {            "_id" : {                "_id" : "$_id",                "from" : "$headers.From"            },            "to" : {"$addToSet" : "$headers.To"}        }    },    {"$unwind" : "$to"},    {        "$group" : {            "_id" : {                "from" : "$_id.from",                "to" : "$to"            },            "count_msg" : {                "$sum" : 1            }        }    },    { "$sort" : {"count_msg" : -1} },    { "$limit" : 5 }]){ "_id" : { "from" : "[e-mail]", "to" : "[e-mail]" }, "count_msg" : 750 }{ "_id" : { "from" : "[e-mail]", "to" : "[e-mail]" }, "count_msg" : 679 }{ "_id" : { "from" : "[e-mail]", "to" : "[e-mail]" }, "count_msg" : 646 }{ "_id" : { "from" : "[e-mail]", "to" : "[e-mail]" }, "count_msg" : 616 }{ "_id" : { "from" : "[e-mail]", "to" : "[e-mail]" }, "count_msg" : 567 }

Q3

> db.messages.find({"headers.Message-ID":"<8147308.1075851042335.JavaMail.evans@thyme>"}).count()1> db.messages.find({"headers.Message-ID":"<8147308.1075851042335.JavaMail.evans@thyme>"}).pretty()db.messages.update({"headers.Message-ID":"<8147308.1075851042335.JavaMail.evans@thyme>"},{$push:{"headers.To":"[e-mail]"}})

Q4

self.posts.update_one( {'permalink': permalink} , {'$inc':{"comments.%s.num_likes"%(comment_ordinal):1}})

PyMongo 版本是 2.5 的情况下，脚本将运行失败，必须要升级到 3.x

Q5

a_1_c_1a_1_b_1a_1_b_1_c_-1c_1

Q6

Remove all indexes from the collection, leaving only the index on _id in placeSet w=0, j=0 on writes

Q7

> db.images.find({tags:"kittens"}).count()49932#!/usr/bin/env pythonimport pymongoconn = pymongo.MongoClient(host="127.0.0.1", port=27017)db = conn.photoalbum_images = []for album in db.albums.find():  album_images.extend(album['images'])album_images = list(set(album_images))images = []for image in db.images.find():  images.append(image['_id'])orphan_images = list(set(images)-set(album_images))print len(orphan_images)for id in orphan_images:  db.images.delete_one({'_id':id})print db.images.count()print db.images.find({'tags':"kittens"}).count()102638973744822

44822

Q8

Maybe, it depends on whether Node 2 has processed the write.

Q9

patient_id

Q10

The query scanned every document in the collection.The query avoided sorting the documents because it was able to use an index's ordering.> db.messages.count()120477

-eof-