Chapter2: MongoDB

This section contain the following items:

• 1.What is MongoDB?

• 2.build MongoDB environment on Ubuntu (14.04)

• 3.MongoDB debug message

• 4.Backup and Restore

• 5.Use mongoDb by using python

• 6.MongoDB的基本操作

1.What is MongoDB?

2.build MongoDB environment on Ubuntu (14.04)

  1)echo “deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen" | sudo tee /etc/apt/sources.list.d/mongo.list:

  建立/etc/apt/sources.list.d/mongo.list,並寫入deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen(作為操作的一部分，APT使用一個檔案列出可獲得套裝軟體的鏡像站台位址件- /etc/apt/sources.list.d

檔案中的各項資訊通常按如下格式列出:deb http://host/debian distribution section1 section2 section3)

  2)sudo apt-key adv --keyserver keyserver.ubuntu.com --recv 7F0CEB10:

    如果公鑰已經上傳到Key Server，可以使用下列指令下載公鑰：
      gpg --keyserver hkp://wwwkeys.us.pgp.net --recv-keys <金鑰指紋>

  3)sudo apt-get update:

    進行伺服器與用戶端的套件表頭清單更新, 在 apt-get update 後,再使用 apt-get dist-upgrade 這樣就能夠將整個系統升級

  4)sudo apt-get install mongodb-10gen

  5)ps -ef | grep mongo:

    確定 mongodb已在執行

  6)ls -ls /usr/bin | grep mongo

  7)ls -ls /etc/init.d | grep mongo

  8)sudo service mogodb start, sudo service mogodb stop, sudo service mogodb restart

3.MongoDB debug message

  1)ERROR: dbpath(data/db) does not exist

    sudo mkdir -p /data/db
    sudo useradd mongo
    sudo passwd mongo
    sudo chown -R mongo:mongo /data/db
    sudo chmod 0755 /data/db
    sudo chown -R $USER /data/db

    可以下ls -ld /data/db/
    ->理論上應該要是： drwxr-xr-x  7 gibber  wheel  238 Aug  5 11:07 /data/db/ （gibber是資料夾owner, wheel是gibber所屬的group）

   2)10309 Unable to create/open lock file: /data/db/mongod.lock errno:

    2014-10-06T12:59:35.802+0530 warning: Failed to connect to 127.0.0.1:27017, reason: errno:111 Connection refused

    2014-10-06T12:59:35.802+0530 Error: couldn't connect to server 127.0.0.1:27017 (127.0.0.1), connection attempt failed at src/mongo/shell/mongo.js:146
exception: connect failed

    rm /var/lib/mongodb/mongod.lock
    sudo service mongod restart

    參考資料：
     1.http://stackoverflow.com/questions/26211671/failed-to-connect-to-127-0-0-127017-reason-errno111-connection-refused
    2.https://gist.github.com/adamgibbons/cc7b263ab3d52924d83b
    3.http://www.marcusoft.net/2014/05/mongodb-and-10309-unable-to-createopen.html
    4.http://stackoverflow.com/questions/24599119/mongodb-not-working-error-dbpath-data-db-does-not-exist

4.Backup and Restore

  Backup:
  1) Enter mongodb command mode by type "mongo" on terminal
  2) use admin
  3) db.runCommand({fsync:1,lock:1})
  4) db.currentOp()
  5) Ctrl + C to back to normal terminal mode 
  6) sudo mongodump -d vote -o ../data/backup
  7) Enter mongodb command mode by type "mongo" on terminal
  8) db.fsyncUnlock()

  Restore:
  1)sudo mongorestore -d vote --drop ../data/backup/vote

  reference:http://mongodbcanred.blogspot.tw/2015/01/mongodbmongodump-mongorestore.html

5.Use mongoDb by using python

   1)Install pymongo:
      import pymongo
      from pymongo import MongoClient
   2)Use monogoDb:
      client = MongoClient('localhost', 27017)
      db = client.{db name}
      collect = db[{collection name}]
      post1 = collect.find_one({"key": "value"})
      post1["key"]

6.MongoDB的基本操作

• 與SQL的名詞對照

• 與SQL指令的對照表

	MongoDB	My SQL
新增	db.collection.find(條件)	select
修改	db.collection.insert(document)	insert
刪除	db.collection.update( criteria, objNew, upsert, multi )	update
查詢	db.collection.remove()	delete

• 新增

• 修改

• 刪除

• 查詢

  • find

    • db.collection.find(query, projection)

      • 定義: 從一個collection中找出documents,並回傳一個cursor物件

      • query:

        • 1. Query Selectors:

             https://docs.mongodb.com/v3.2/reference/operator/query/
        • 2.Update Operators:

          https://docs.mongodb.com/v3.2/reference/operator/update/
        • 3.Aggregation Pipeline Operators:

          https://docs.mongodb.com/v3.2/reference/operator/aggregation/
        • 4.Query Modifiers:

          https://docs.mongodb.com/v3.2/reference/operator/query-modifier/
      • projection:

        • projection決定了哪些欄位要被回傳

      • cursor:

        • 一個指向a set of query的指標, 使用者可用迭代的方式從cursor取回查詢結果. 預設timeout為10分鐘

        • 取回方式

          • 1.手動迭代

            var myCursor = db.users.find( { type: 2 } );
            while (myCursor.hasNext(){
              print(tojson(myCursor.next()));
            }
            
            或是:
            
            var myCursor = db.users.find( { type: 2 } );
            while (myCursor.hasNext()) {
               printjson(myCursor.next());
            }
            
            或是:
            
            var myCursor =  db.users.find( { type: 2 } );
            myCursor.forEach(printjson);

          • 2.轉為array

             var myCursor = db.inventory.find( { type: 2 } );
              var documentArray = myCursor.toArray();
              var myDocument = documentArray[3];

      • example:

        • 取出投過票的人

          collection.find({
            $or: [{
                candidateId: {
                    $ne: 99
                }
            }, {
                candidateId2: {
                    $ne: 99
                }
            }]
          }, {
            mail: 1
          }).toArray(function(err, items) {
              mongodb.close();
                if (err) {
                  console.log("User.getVotedUsers:" + err);
                  callback(err);
                }
              console.log(items);
              callback(null, items);
              //res.send(items);
          });

    • reference: https://docs.mongodb.com/getting-started/shell/query/
  • findOne