by Oscar Ivarsson

MongoDB

Show-Off

What is it?

Type: Document Database

Designed as a scalable database (humongous)

Open Source

Released: 2009

Notation

Database

Collection

RDBMS

Schema

Instance

MongoDB

Instance

Table

Document

Row

Example

> printjson(db.towns.findOne({"_id":ObjectId("4d0b6da3bb30773266f39fea")}))
{
    "_id":ObjectId("4d0b6da3bb30773266f39fea"),
    "country": {
        "$ref": "countries",
        "$id": ObjectId("4d0e6074deb899526a8309e")
    },
    "famous_for": [
        "beer",
        "food"
    ],
    "last_census": "Thu Sep 20 2007 00:00:00 GMT    -0700 (PDT)",
    "mayor": {
        "name": "Sam Adams",
        "party": "D"    
    },
    "name": "Portland",
    "population": 582000,
    "state": "OR"
}

Stored as BSON - Shown as JSON

Database: "db"
Collection: "towns"
Document: Between the brackets
Identifier: "_id"

0-3: Timestamp
4-6: Client Machine ID
7-8: Client Process ID
9-11: Incremented Counter

Notations

ObjectId (12 bytes)

Examples

> db.test.insert({color: "Red"})
> db.test.insert({shape: "Triangle"})

Insert

> db.test.find()
{ 
    "_id" : ObjectId("55ee924b34ec1a858b481962"),
    "color" : "Red"
}
{
    "_id" : ObjectId("55ee927f34ec1a858b481963"),
    "shape" : "Triangle"
}

Find

Examples

> db.test.find({ "_id" : ObjectId("55ee927f34ec1a858b481963") })
{ 
    "_id" : ObjectId("55ee927f34ec1a858b481963"),
    "shape" : "Triangle"
}

Find by ID

> db.test.find( { "shape": "Triangle"} )
{ 
    "_id" : ObjectId("55ee927f34ec1a858b481963"),
    "shape" : "Triangle"
}

Find by field (slower..)

> db.test.find( function() {
    return this.shape == "Triangle";
  })

{ 
    "_id" : ObjectId("55ee927f34ec1a858b481963"),
    "shape" : "Triangle"
}

Find by function (slowest!)

Query Commands

Command	Description
$regex	Match by regular expression
$lt	Less than
$in	Match any elements in an array
$exists	Check for existence of a field

Examples for find

Command	Description
$set	Sets the given field with a given value
$push	Adds the value to an array
$pull	Removes matching value from array

Examples for update

References

Mongo is not built for performing joins because of its distributed nature!

Documents can however reference eachother.

> db.towns.update(
    { _id : ObjectId("4d0ada87bb30773266f39fe5") },
    { $set : { country: { $ref: "countries", $id: "us" } } }
  )

THEN

> var portland = db.towns.findOne({ _id : ObjectId("4d0ada87bb30773266f39fe5") })
> db.countries.findOne({ _id: portland.country.$id })

OR

> 
db[ portland.country.$ref ].findOne({ _id: portland.country.$id })

Performance

Query performance can be increased in MongoDB by using indexing.

Full collection scan

B-tree indexing

Scanned objects: 1 000 000

Scanned objects: 1

Execution Time 1st: 470 ms

Execution Time 2nd: 365 ms

Execution Time 1st: 5 ms

Execution Time 2nd: 0 ms

> populatePhones(800, 809, 5550000, 5650000)
> db.phones.find().limit(1)

{ 
    "_id" : 18005550000, 
    "components" : { 
        "country" : 1,
        "area" : 800,
        "prefix" : 555,
        "number" : 5550000 },
        "display" : "+1 800-5550000" 
}