Experimenting with Mongodb

  A NoSQL is a popular type of database system is Mongodb. The installation and working inn general shall be further.

 

 Installing Mongodb

I am using ubuntu 11.10, for which the steps are as follow:-

• In a terminal type the following command to import the 10gen public GPG key:

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

• create a file /etc/apt/sources.list.d/10gen.list and write the following in the file and save.

For upstart users- deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen

For SysV users- deb http://downloads-distro.mongodb.org/repo/debian-sysvinit dist 10gen

For those who are confused what are upstart ans SysV it is nothing but the different in version of ubuntu/debian. Upstart is an event-based replacement for the /sbin/init daemon which handles starting of tasks and services during boot, stopping them during shutdown and supervising them while the system is running.

The "init" or "system initialisation" process on Unix and Linux systems has process ID (PID) "1". That is to say, it is the first process to start when the system boots (ignoring the initrd/initramfs). As the quote shows, Upstart is an "init" replacement for the traditional Unix "System V" "init" system.

• Ok now to reload your repository type the following in the command prompt.

         sudo apt-get update

• now to install the packages.

sudo apt-get install mongodb-10gen

Now to work with Mongo

For starting the mongodb type-

sudo services mongodb start

For stopping type-

sudo services mongodb stop

To restart-

 

sudo services mongodb restart

Now to use to use Mongodb like SQL we start by typing “mongo” in the terminal. The assigning and saving values is simple. The commands and their outputs are shown as below:-

mongo
MongoDB shell version: 1.8.2
Fri Aug 10 12:34:22 *** warning: spider monkey build without utf8 support.  consider rebuilding with utf8 support
connecting to: test
> db.things.save({name:"anjali"});
> db.things.find();
{ "_id" : ObjectId("5023e84c7c4542be6849ac20"), "name" : "mongo" }
{ "_id" : ObjectId("5024b2944bed5e5a6dba42e1"), "name" : "anjali" }
>

Data can be iteratively added to the db using the command below.

> for(var i=1;i<=20;i++) db.things.save({x:4,j:i});
> db.things.find();
{ "_id" : ObjectId("5023e84c7c4542be6849ac20"), "name" : "mongo" }
{ "_id" : ObjectId("5024b2944bed5e5a6dba42e1"), "name" : "anjali" }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e2"), "x" : 4, "j" : 1 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e3"), "x" : 4, "j" : 2 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e4"), "x" : 4, "j" : 3 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e5"), "x" : 4, "j" : 4 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e6"), "x" : 4, "j" : 5 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e7"), "x" : 4, "j" : 6 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e8"), "x" : 4, "j" : 7 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e9"), "x" : 4, "j" : 8 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ea"), "x" : 4, "j" : 9 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42eb"), "x" : 4, "j" : 10 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ec"), "x" : 4, "j" : 11 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ed"), "x" : 4, "j" : 12 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ee"), "x" : 4, "j" : 13 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ef"), "x" : 4, "j" : 14 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f0"), "x" : 4, "j" : 15 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f1"), "x" : 4, "j" : 16 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f2"), "x" : 4, "j" : 17 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f3"), "x" : 4, "j" : 18 }
has more
>

The has more means that the first 20 are displayed in the list. To view more we have a short command it which displays the rest of the elements in the list.

> it
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f4"), "x" : 4, "j" : 19 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f5"), "x" : 4, "j" : 20 }
>

To access data from a query, it is slightly different way than in sql. The find can be done using a while loop as well. Given below:-

> var icon = db.things.find();
> while(icon.hasNext()) printjson(icon.next());
{ "_id" : ObjectId("5023e84c7c4542be6849ac20"), "name" : "mongo" }
{ "_id" : ObjectId("5024b2944bed5e5a6dba42e1"), "name" : "anjali" }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e2"), "x" : 4, "j" : 1 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e3"), "x" : 4, "j" : 2 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e4"), "x" : 4, "j" : 3 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e5"), "x" : 4, "j" : 4 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e6"), "x" : 4, "j" : 5 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e7"), "x" : 4, "j" : 6 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e8"), "x" : 4, "j" : 7 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e9"), "x" : 4, "j" : 8 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ea"), "x" : 4, "j" : 9 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42eb"), "x" : 4, "j" : 10 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ec"), "x" : 4, "j" : 11 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ed"), "x" : 4, "j" : 12 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ee"), "x" : 4, "j" : 13 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ef"), "x" : 4, "j" : 14 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f0"), "x" : 4, "j" : 15 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f1"), "x" : 4, "j" : 16 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f2"), "x" : 4, "j" : 17 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f3"), "x" : 4, "j" : 18 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f4"), "x" : 4, "j" : 19 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f5"), "x" : 4, "j" : 20 }
>
 

We can use a forEach command just like while loop. In the following screenshot how it works.

> db.things.find().forEach(printjson);
{ "_id" : ObjectId("5023e84c7c4542be6849ac20"), "name" : "mongo" }
{ "_id" : ObjectId("5024b2944bed5e5a6dba42e1"), "name" : "anjali" }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e2"), "x" : 4, "j" : 1 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e3"), "x" : 4, "j" : 2 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e4"), "x" : 4, "j" : 3 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e5"), "x" : 4, "j" : 4 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e6"), "x" : 4, "j" : 5 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e7"), "x" : 4, "j" : 6 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e8"), "x" : 4, "j" : 7 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42e9"), "x" : 4, "j" : 8 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ea"), "x" : 4, "j" : 9 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42eb"), "x" : 4, "j" : 10 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ec"), "x" : 4, "j" : 11 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ed"), "x" : 4, "j" : 12 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ee"), "x" : 4, "j" : 13 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42ef"), "x" : 4, "j" : 14 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f0"), "x" : 4, "j" : 15 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f1"), "x" : 4, "j" : 16 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f2"), "x" : 4, "j" : 17 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f3"), "x" : 4, "j" : 18 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f4"), "x" : 4, "j" : 19 }
{ "_id" : ObjectId("5024b93c4bed5e5a6dba42f5"), "x" : 4, "j" : 20 }
>

You are also allowed to treat icon or cursors as arrays by the following command.

> var cursor = db.things.find();
> printjson(cursor[4]);
{ "_id" : ObjectId("4c220a42f3924d31102bd858"), "x" : 4, "j" : 3 }
 

You can also convert to an array by using:-

 
> var arr = db.things.find().toArray();
> arr[5];
{ "_id" : ObjectId("4c220a42f3924d31102bd859"), "x" : 4, "j" : 4 }
 

Using as Query

In sql queries we use sel * from table where condition. and for a particular case as sel element from table where condition.- The similar notation in mongo are -

db.things.find(condition).forEach(printjson);

 db.things.find(specific condition(s)).forEach(printjson);

findOne() 
 
  Lets you retrieve one document via findOne function.

> printjson(db.things.findOne({name:"mongo"}));
{ "_id" : ObjectId("4c2209f9f3924d31102bd84a"), "name" : "mongo" }
 

Limiting the result

 
 This is done using limit function as follows.

> db.things.find().limit(3);
{ "_id" : ObjectId("4c2209f9f3924d31102bd84a"), "name" : "mongo" }
{ "_id" : ObjectId("4c2209fef3924d31102bd84b"), "x" : 3 }
{ "_id" : ObjectId("4c220a42f3924d31102bd856"), "x" : 4, "j" : 1 }

NoSQL and Mongodb are not yet very popular substitutes to SQL but definitely strong scalable comtemporary to RDBMS.