# 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:
* 2.Update Operators:
* 3.Aggregation Pipeline Operators:
* 4.Query Modifiers:
* 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:
* findOne