Ruby Programming Tutorial - Lesson 40 - Javascript Object Notation JSON in Ruby

JavaScript Object Notation (JSON)

JSON is a lightweight data-interchange format. It is easy for us humans to read and write. Plus, equally simple for machines to generate or parse. JSON is completely language agnostic, making it the ideal interchange format.

Built on two universally available structures:

1. A collection of name/value pairs. Often referred to as an object, hash table, record, struct, keyed list, or associative array.
2. An ordered list of values. More commonly called an array, vector, sequence or list.

JSON is similar to Hashes in Ruby, but it's not a ruby Hash, that is why we need to parse it into a ruby hash, in order to use it, in our ruby programs. The reason why it is not a ruby hash, is because it uses keys instead of symbols :) and it comes from a different world, the world of Javascript :)

Notice that where we have Symbols (:fullname => "bilal" or fullname: "bilal') and a corresponding values in hashes, in JSON there exist no symbols, but rather they are called keys "fullname" : "Bilal Haider", key is surrounded by double quotes .. so no symbols, no hashes :)

Because JSON is widely used in interchanging data, across applications, we need to learn to handle this Data Notation in ruby, that's why we need to learn to work with it :)

{
     "fullname" : "Bilal Haider"
     "age": 27
     "address": "Islamabad Pakistan"
}

Here is the qualities of JSON objects

1. JSON objects are surrounded by curly braces {}.
2. JSON objects are written in key/value pairs.
3. Keys must be strings, and values must be a valid JSON data type (string, number, object, array, boolean or null).
4. Keys and values are separated by a colon.
5. Each key/value pair is separated by a comma.

Here is another example of a more complex Json Object

{
    "name":"John",
    "age":30,
    "cars": {
        "car1":"Ford",
        "car2":"BMW",
        "car3":"Fiat"
    }
 } 

Ruby provides us a module called JSON which has few methods, which we can use to handle JSON data objects, we call it parsing Json objects

Lets us see how we do that, by taking an example :)

The Task

Create a ruby program that reads Json data from file, and parse it into a ruby hash, so that each data item can be used in ruby programs

require 'json'

_data = File.read("data")
puts "Displaying Data as is: "
puts _data

_myhash = JSON.parse(_data)

puts "Displayed Hashed data: "
puts _myhash

## Once your data is parsed into a hash
## you can use it like so 

puts _myhash["name"]
puts _myhash["age"]
puts _myhash["cars"]

We have a file named data which has dummy data, which we want to parse into a ruby hash

It is possible to get JSON data from a website url or link, which is a method to share your application's data with the world, where other programmers can use your data in their applications.
Here is the result of our ruby program :)

By following same approach, we can also create JSON objects, and share our application's data, with the world..

which other people can parse into hashes and create awesome ruby programs for themselves or for to share with the world.

How to convert my hash into JSON and save that data in a text file ?

require 'json'

my_hash = {name: "bilal", age: "27", hobbies: {first: "programming", second: "ruby"}}
_mydata = JSON.generate(my_hash)

File.open("data2", "w") do |f|
    f.print _mydata
end

Notice that here, we have a data in the form of a hash, and we converted into a JSON object, which we then using Filing store in our file called data2

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