Basics of MongoDB

Introduction

• MongoDB is a fast document-oriented database
• replaces the concept of a "row" with a more flexible model - the "document"
• convenient data storage for modern object-oriented languages
• no predefined schemas
• no transactions
• no SQL
• supports indexes
• easy to scale out horizontally

Getting Started

• document is a basic unit of data (like row in RDBMS)
• collection = table
• multiple databases in single instance
• _id in every document, unique within collection
• JavaScript shell for administration and data manipulation

Documents

• document is an ordered set of keys with associated values
• representation of a document varies by programming language (map; hash - Perl, Ruby; dictionary - Python)
• objects in JavaScript {key:value}
• example {"company" : "NobleProg", "training" : "MongoDB for Developers"}
• key is a string, any UTF-8 is allowed (except \0 . $)
• type-sensitive {"age" : 3}, {"age" : "3"}
• case-sensitive {"age" : 3}, {"Age" : 3}
• documents cannot contain duplicated keys
• key/value pairs are ordered {"x" : 1, "y" : 1} != {"y" : 1, "x" : 1}
  • order does not usually matter, MongoDB can reorder keys

{
  "_id" : ObjectId("545a414c7907b2a255b156c5"),
  "Name" : "Sean Connery",
  "Nationality" : "Great Britain",
  "BirthDate" : ISODate("1930-08-25T00:00:00Z"),
  "BirthYear" : 1930,
  "Occupation" : [
    "Actor",
    "Director",
    "Producer"
  ],
  "Movie" : [
    {
      "_id" : ObjectId("545a5f167907b2a255b156c7"),
      "Title" : "Dr. No"
    },
    {
      "_id" : ObjectId("545a5f317907b2a255b156c8"),
      "Title" : "From Russia with Love"
    },
    {
      "_id" : ObjectId("545a5ed67907b2a255b156c6"),
      "Title" : "Never Say Never Again"
    }
  ],
  "BirthPlace" : {
    "Country" : "United Kingdom, Scotland",
    "City" : "Edinburgh"
  }
}

Collections

• a group of documents
• dynamic schemas
  • {"company" : "NobleProg"}
  • {"age" : 5}
• why should we use more than one collection?
  • nightmare for developers
  • much faster to get a list of collections than extracting document types from collections
  • grouping documents of the same kind
  • indexes
• collection name is a string, any UTF-8 is allowed except:
  • empty string, start with "system." prefix, contain \0 character, $ character
• subcollections separated by the . character
  • example GridFS (fs.files, fs.chunks)

Databases

• database is a group of collections
• one database = one application
• separated databases for different applications, users
• database name is a alphanumeric string, case sensitive, max 64 bytes, empty string is not allowed
• database name will end up as file on filesystem (this explains restrictions)
• special databases: admin (root database), local (never replicated), config (when sharding)
• namespace is a concatenation of database and collection name (fully qualified collection name)
  • max 121 bytes, shold be less than 100

Getting and Starting MongoDB

1. Installation on Windows
   • http://docs.mongodb.org/manual/tutorial/install-mongodb-on-windows/
2. Installation on Ubuntu
   • http://docs.mongodb.org/manual/tutorial/install-mongodb-on-ubuntu/

CRUD

Create

use NobleProg
person = {"Name" : "Sean Connery", "Nationality" : "Great Britain"}
db.people.insert(person)

Read

db.people.find()
db.people.findOne()
db.people.find().pretty() // .pretty() is the default now, so can be omitted

Update

personUp = {"Occupation" : "Actor"}
db.people.update({"Name" : "Sean Connery"}, {$set: personUp})
db.people.findOne()

Delete

db.people.remove({"Name" : "Sean Connery"})
db.people.remove({})
db.people.findOne()

Data Types

• JSON-like documents
  • 6 data types: null, boolean, numeric, string, array, object
• MongoDB adds support for other datatypes
  • null {"x" : null}
  • boolean {"x" : true}
  • number (by default 64-bit floating point numbers) {"x" : 1.4142}
    • 4-byte integers {"x" : NumberInt(141)}
    • 8-byte integers {"x" : LongInt(141)}
  • string (any UTF-8 character) {"x" : "NobleProg"}
  • date (stored as milliseconds from Linux epoch) {"x" : new Date()}
  • regular expressions (in queries) {"x" : /bob/i}
  • array {"x" : [1.4142, true, "training"]}
  • embedded documents {"x" : {"y" : 100}}
  • ObjectId {"x" : ObjectId("54597591bb107f6ef5989771")}
  • binary data (for non-UTF-8 strings)
  • code {"x" : function() {/*...*/}}

_id and ObjectId

• every document in MongoDB must have _id
• can be any type but it defaults to ObjectId
• unique values in a single collection
• ObjectId is designed to lightweight and easy to generate
  • 12-bytes of storage (24 hexidecimal digits)
    • timestamp - byte 0-3
    • machine - byte 4-6
    • PID - byte 7-8
    • increment - byte 9-11
  • _id is generated automatically if not present in document

MongoDB Shell

$ mongo
MongoDB shell version: 4.0.6
connecting to: test
>

$ mongo HostName:PortNumber/DatabaseName
$ mongo localhost:27017/test

$ mongo --nodb
> conn = new Mongo("localhost:27017")
connection to localhost27017
> db = conn.getDB("NobleProg")
NobleProg

Using help

• mongo is a JavaScript shell, help is available in JavaScript on-line documentation
• use built-in help for MongoDB-specific functionality
• type function name without parentheses to see what the function is doing
  

> help
    db.help()            help on db methods
    db.mycoll.help()     help on collections methods
    ...
    exit                 quit mongo shell
>
> db.NobleProg.stats
function ( scale ){
    return this._db.runCommand( { collstats : this._shortName , scale : scale } );
}
>
> db.NobleProg.stats()
{ "ok" : 0, "errmsg" : "Collection [test.NobleProg] not found." }
>

Running Scripts

• mongo can execute JavaScript files
• scripts have access to all global variables (e.g. "db")
• shell helpers (e.g. "show collections") do not work from files; use valid JavaScript equivalents (e.g. "db.getCollectionNames()")
• use --quiet to hide "MongoDB shell version..." when executing script
• use load() to run script directly from Mongo Shell
• use .mongorc.js for frequently-loaded scripts
  • located in user home directory, run when starting up the shell, --norc to disable it
  • useful also to customize prompt

$ mongo script.js
MongoDB shell version: 4.0.6
connecting to: test
script.js was executed successfully!
$
$ mongo --quiet script.js
script.js was executed successfully!
$
$ mongo
MongoDB shell version: 4.0.6
connecting to: test
> load("script.js")
script.js was executed successfully!
>

Editing Complex Variables

• limited multiline support in the shell
• external editors are allowed
• EDITOR="/usr/bin/gedit"
• EDITOR="c:\\windows\\notepad.exe"

$ mongo --quiet
> EDITOR="c:\\windows\\notepad.exe"
> use training
switched to db training
> person = db.people.findOne()
{ "_id" : ObjectId("54568445cfc7c83518fa5430"), "Name" : "Sean Connery" }
> edit person
> person
{ "_id" : ObjectId("54568445cfc7c83518fa5430"), "Name" : "Sean Connery", "Nationality" : "Great Britain" }
> db.people.save(person)