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From the hp: “MongoDB (from “humongous”) is a scalable, high-performance, open source NoSQL database. Written in C++, features”

  • Document-Oriented Storage (JSON-style documents with dynamic schemas offer simplicity and power)
  • Full Index Support (Index on any attribute)
  • Replication & High Availability (Mirror across LANs and WANs)
  • Auto-Sharding (Scale horizontally without compromising functionality)
  • Querying
  • Fast In-Place Updates
  • Map/Reduce
  • GridFS
  • Commercial Support

This page aims to be a MongoDB “hello world” example, for more info read

Differences to traditional DBMS

MongoDB does not support transactions. Atomic operations are supported.

Getting started

sudo apt-get install mongodb

will pull in all dependencies, install and start the database.

If required, adjust settings in /etc/mongodb.conf (like IP binding or port)

Start/stop database

sudo service mongodb stop
sudo service mongodb start

Login to database

An easy way is the mongo interactive shell. In a terminal, type


This connects to database “test”.

Usage examples

The information below comes from the MongoDB manual

Use a specific database

To use a specific database, say “accounts”, login to mongo and issue

>use accounts

If database “accounts” does not exist yet, it will be created.

List all existing databases:

>show dbs


MongoDB collections can be compared to RDBS tables. Collections are named groupings of documents.

Login to a specific database and list existing collections:

>use accounts
>show collections

As with databases, the first time you access a collection, it will be automatically be created for you.

Insert documents

As mentioned before, MongoDB is document-oriented. Whereas you think of rows in RDBMS, you think of documents in MongoDB. More specifically, MongoDB documents are in JSON format.

Insert one document

>{"name":"alice","type":"withdrawal", "amount": 30})

or bulk insert (supported in shell since v2.2)

>[{"name":"alice","type":"deposit", "amount": 500}, {"name":"alice","type":"withdrawal", "amount": 50}, {"name":"bob","type":"withdrawal", "amount": 20}, {"name":"bob","type":"withdrawal", "amount": 60}])


Change transaction type to “deposit” where name=bob and amount 60

> db.transactions.update({"name":"bob", "amount":60}, {$set : {"type":"deposit"}})

Delete documents

db.transactions.drop() 	//drop the entire transactions collection
db.transactions.remove() //remove all objects from the collection
db.transactions.remove( { name : "sara" } )  //remove objects from the collection where name is sara

Retrieve data

Get all documents

> db.transactions.find()

With WHERE clause

Alice's money transactions:

> db.transactions.find({"name" : "alice"})

Only specific fields

Show only type and amount fields

> db.transactions.find({}, {"type":true, "amount":true, "_id":false})

Limit result to x rows

> db.transactions.find({}, {}).limit(2)

Sort results

sort by name ascending, amount descending

> db.transactions.find( {},{}).sort({"name":1,"amount":-1})


Run ensureIndex(), which builds the index ONLY if it does not already exist.


View existing indizes


The manual has more details.

Simple analyses

Count lines

> db.transactions.count() 
// or with a WHERE clause
> db.transactions.count({"name":"alice"}) 

Calculate sum

How much did all users withdraw?

> {
   "key": {"name":true} , 
   "cond": {"type":"withdrawal"}, 
   "reduce": function (obj,prev) { prev.csum += obj.amount; }, 
   "initial": { csum: 0 } 
}  )

Calculate average

Distinct values

> db.transactions.distinct("name")

Analyse query

Use explain() to get statistics about a query, e.g. check “millis” for the query runtime in milliseconds.

NOTE: during the execution of explain(), the actual query is being run! So if the query takes lots of time, explain() will take a long time, too.

> db.transactions.find({},{"name":true, "amount":"true"}).explain()
	"cursor" : "BasicCursor",
	"isMultiKey" : false,
	"n" : 6,
	"nscannedObjects" : 6,
	"nscanned" : 6,
	"nscannedObjectsAllPlans" : 6,
	"nscannedAllPlans" : 6,
	"scanAndOrder" : false,
	"indexOnly" : false,
	"nYields" : 0,
	"nChunkSkips" : 0,
	"millis" : 0,
	"indexBounds" : {
	"server" : "ankh:27017"
mongodb.txt · Last modified: 2012/11/22 10:51 by mantis