MongoDB Introduction

From WikiOD

Remarks[edit | edit source]

  • Data in the world started to grow tremendously after mobile application came in the market. This huge amount of data became almost impossible to handle with traditional relational database - SQL. NoSQL databases are introduced to handle those data where much more flexibility came like variable number of columns for each data.
  • MongoDB is one of the leading NoSQL databases. Each collection contains a number of JSON documents. Any data model that can be expressed in a JSON document can be easily stored in MongoDB.
  • MongoDB is a server-client database. Server usually runs with the binary file mongod and client runs with mongo.
  • There is no join operation in MongoDB prior to v.3.2, for various philosophical and pragmatic reasons. But Mongo shell supports javascript, so if $lookup is not available, one can simulate join operations on documents in javascript before inserting.
  • To run an instance in production environment, it's strongly advised to follow the Operations Checklist.

Versions[edit | edit source]

Version Release Date
3.4 2016-11-29
3.2 2015-12-08
3.0 2015-03-03
2.6 2014-04-08
2.4 2013-03-19
2.2 2012-08-29
2.0 2011-09-12
1.8 2011-03-16
1.6 2010-08-31
1.4 2010-03-25
1.2 2009-12-10

Execution of a JavaScript file in MongoDB[edit | edit source]

./mongo localhost:27017/mydb myjsfile.js

Explanation: This operation executes the myjsfile.js script in a mongo shell that connects to the mydb database on the mongod instance accessible via the localhost interface on port 27017. localhost:27017 is not mandatory as this is the default port mongodb uses.

Also, you can run a .js file from within mongo console.

>load("myjsfile.js")

Making the output of find readable in shell[edit | edit source]

We add three records to our collection test as:

> db.test.insert({"key":"value1","key2":"Val2","key3":"val3"})
WriteResult({ "nInserted" : 1 })
> db.test.insert({"key":"value2","key2":"Val21","key3":"val31"})
WriteResult({ "nInserted" : 1 })
> db.test.insert({"key":"value3","key2":"Val22","key3":"val33"})
WriteResult({ "nInserted" : 1 })

If we see them via find, they will look very ugly.

> db.test.find()
{ "_id" : ObjectId("5790c5cecae25b3d38c3c7ae"), "key" : "value1", "key2" : "Val2
", "key3" : "val3" }
{ "_id" : ObjectId("5790c5d9cae25b3d38c3c7af"), "key" : "value2", "key2" : "Val2
1", "key3" : "val31" }
{ "_id" : ObjectId("5790c5e9cae25b3d38c3c7b0"), "key" : "value3", "key2" : "Val2
2", "key3" : "val33" }

To work around this and make them readable, use the pretty() function.

> db.test.find().pretty()
{
        "_id" : ObjectId("5790c5cecae25b3d38c3c7ae"),
        "key" : "value1",
        "key2" : "Val2",
        "key3" : "val3"
}
{
        "_id" : ObjectId("5790c5d9cae25b3d38c3c7af"),
        "key" : "value2",
        "key2" : "Val21",
        "key3" : "val31"
}
{
        "_id" : ObjectId("5790c5e9cae25b3d38c3c7b0"),
        "key" : "value3",
        "key2" : "Val22",
        "key3" : "val33"
}
>

Complementary Terms[edit | edit source]

SQL Terms MongoDB Terms
Database Database
Table Collection
Entity / Row Document
Column Key / Field
Table Join Embedded Documents
Primary Key Primary Key (Default key _id provided by mongodb itself)

Installation[edit | edit source]

To install MongoDB, follow the steps below:

For Mac OS:

  • There are two options for Mac OS: manual install or homebrew.
  • Installing with homebrew:

Type the following command into the terminal:

$ brew install mongodb
  • Installing manually:

Download the latest release here. Make sure that you are downloading the appropriate file, specially check whether your operating system type is 32-bit or 64-bit. The downloaded file is in format tgz.

Go to the directory where this file is downloaded. Then type the following command:

$ tar xvf mongodb-osx-xyz.tgz

Instead of xyz, there would be some version and system type information. The extracted folder would be same name as the tgz file. Inside the folder, their would be a subfolder named bin which would contain several binary file along with mongod and mongo.

By default server keeps data in folder /data/db. So, we have to create that directory and then run the server having the following commands:

$ sudo bash
# mkdir -p /data/db
# chmod 777 /data
# chmod 777 /data/db
# exit

To start the server, the following command should be given from the current location:

$ ./mongod

It would start the server on port 27017 by default.

To start the client, a new terminal should be opened having the same directory as before. Then the following command would start the client and connect to the server.

$ ./mongo

By default it connects to the test database. If you see the line like connecting to: test. Then you have successfully installed MongoDB. Congrats! Now, you can test Hello World to be more confident.

For Windows:

Download the latest release here. Make sure that you are downloading the appropriate file, specially check whether your operating system type is 32-bit or 64-bit.

The downloaded binary file has extension exe. Run it. It will prompt an installation wizard.

Click Next.

Accept the licence agreement and click Next.

Select Complete Installation.

Click on Install. It might prompt a window for asking administrator's permission. Click Yes.

After installation click on Finish.

Now, the mongodb is installed on the path C:/Program Files/MongoDB/Server/3.2/bin. Instead of version 3.2, there could be some other version for your case. The path name would be changed accordingly.

bin directory contain several binary file along with mongod and mongo. To run it from other folder, you could add the path in system path. To do it:

  • Right click on My Computer and select Properties.
  • Click on Advanced system setting on the left pane.
  • Click on Environment Variables... under the Advanced tab.
  • Select Path from System variables section and click on Edit....
  • Before Windows 10, append a semi-colon and paste the path given above. From Windows 10, there is a New button to add new path.
  • Click OKs to save changes.

Now, create a folder named data having a sub-folder named db where you want to run the server.

Start command prompt from their. Either changing the path in cmd or clicking on Open command window here which would be visible after right clicking on the empty space of the folder GUI pressing the Shift and Ctrl key together.

Write the command to start the server:

> mongod

It would start the server on port 27017 by default.

Open another command prompt and type the following to start client:

> mongo

By default it connects to the test database. If you see the line like connecting to: test. Then you have successfully installed MongoDB. Congrats! Now, you can test Hello World to be more confident.

For Linux: Almost same as Mac OS except some equivalent command is needed.

  • For Debian-based distros (using apt-get):

Import MongoDB Repository key.

$ sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv EA312927
gpg: Total number processed: 1\
gpg:               imported: 1  (RSA: 1)

Add repository to package list on Ubuntu 16.04.

$ echo "deb http://repo.mongodb.org/apt/ubuntu xenial/mongodb-org/3.2 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.2.list

on Ubuntu 14.04.

$ echo "deb http://repo.mongodb.org/apt/ubuntu trusty/mongodb-org/3.2 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.2.list

Update package list.

$ sudo apt-get update

Install MongoDB.

$ sudo apt-get install mongodb-org
  • For Red Hat based distros (using yum):

use a text editor which you prefer.

$ vi /etc/yum.repos.d/mongodb-org-3.4.repo

Paste following text.

[mongodb-org-3.4]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/3.4/x86_64/
gpgcheck=1
enabled=1
gpgkey=https://www.mongodb.org/static/pgp/server-3.4.asc

Update package list.

$ sudo yum update

Install MongoDB

$ sudo yum install mongodb-org

Basic commands on mongo shell[edit | edit source]

Show all available databases:

show dbs;

Select a particular database to access, e.g. mydb. This will create mydb if it does not already exist:

use mydb;

Show all collections in the database (be sure to select one first, see above):

show collections;

Show all functions that can be used with the database:

db.mydb.help();

To check your currently selected database, use the command db

> db
mydb

db.dropDatabase() command is used to drop a existing database.

db.dropDatabase()

Hello World[edit | edit source]

After installation process, the following lines should be entered in mongo shell (client terminal).

> db.world.insert({ "speech" : "Hello World!" });
> cur = db.world.find();x=cur.next();print(x["speech"]);

Hello World!

Explanation:

  • In the first line, we have inserted a { key : value } paired document in the default database test and in the collection named world.
  • In the second line we retrieve the data we have just inserted. The retrieved data is kept in a javascript variable named cur. Then by the next() function, we retrieved the first and only document and kept it in another js variable named x. Then printed the value of the document providing the key.

Credit:Stack_Overflow_Documentation