Week1

#NOTES FROM THE COURSE

#Week 1: Introduction and Overview

What are we going to do?

Abstract

We are going to build a blog engine, written in Java, which is connected to a MongoDB database. Since this course is a MongoDB cousre, most of the Java code is written for us, so we can concentrate on the database.

Application architecture - Components

• Database: MongoDB
• Application:
  • Spark framework: URL mapping, lightweight web framework
  • Freemarker framework: Templating framework, we will use to create HTML templates with placeholders
  • MongoDB Java driver
    • Communicates with the database via TCP

Introduction to MongoDB

What is MongoDB?

• Non-rational database
• Stores JSON-s (actually BSON-s, which are the binary representation of JSON)
• Documents can have hierarchy: nested lists and dictionaries
• Schemaless
• Lightweight

Relative to relational DBMS-es

MongoDB was designed to find a good compromise between functionality and scalability. Result: MongoDB scales better, than relational DBMS-es, but has less functionality (eg.: no joins, no transactions, BUT document modification is atomic)

Mongo program

We can access the DBMS directly (without drivers) via the mongo shell program, which has a JavaScript interface. You can start mongo shell by typing mongo into the terminal. Information about it's methods: http://docs.mongodb.org/manual/reference/method/

Playing with MongoDB

• Start MongoDB: mongod --dbpath <path to directory> (Changed the default data directory)
• Start mongo: mongo (Connects to the default database, test)

Note to self:
  echo $PATH   
  PATH=$PATH:<path to directory>

• List avaiable databases: show dbs (Empty databases are not displayed)
• Change to database: use <database name> (Creates if not exsists)
• Save new item: db.<Collection name>.save(<JSON>)
• List all collections of the database: show collections

Use TAB for autocompletion

• List items in a collection: db.<Collection name>.find()

The documents we store in our database are placed in collections. A collection is like a table in a relational database, but it's schemaless and stores JSON documents instead of records.
We can see, that every item has an attribute called _id, it is a unique identifier, generated if not given, an index is built on it.

JSON

Introduction

MongoDB stores JSON-s, which stands for JavaScript Object Notation. It is a commonly used data-interchange format, it's standardized.

Syntax: http://json.org/

Good to know

• Using "" in the keys is not required (at least in MongoDB), but recommended
• {} -> valid JSON
• {"a" : {"a" : 1}} -> valid JSON

Frameworks

The 2 frameworks which we are going to use are:

• Spark
• Freemarker

Spark

• micro web framework for Java applications
• helps mapping URL-s
• it has a built-in webserver called Jetty
• info: http://sparkjava.com/

Freemaker

• Java template engine to generate text outputs based on templates
• we will use it to generate HTML outputs
• info: http://freemarker.org/index.html