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JSON: Javascript Object Notation

What is JSON?

JSON is a data format used to transfer information over the web
It looks very similar to ruby hashes but is a little different

  1. JSON keys are always strings
  2. Pairs are denoted by : instead of =>

Example JSON

When we receive JSON from the web, it is always a string

'{
  "person_1": {
    "age": 1,
    "first_name": "Tommy",
    "last_name": "Pickles"
    "sister": "person_2"
  },
  "person_2": {
    "age": 3,
    "first_name": "Angelica",
    "last_name": "Pickles",
    "brother": "person_1"
  }
}'

When you see JSON in Ruby, it may look like:
"{ \"age\": 1, \"name\": \"Tommy Pickles\" }"

The backslashes are "escaping" the quotations. Otherwise, the computer would think the "age" quotes was the end of the string!

Parsing(reading) JSON

In Ruby, when we get JSON it will be a string. We parse it with the JSON library

require 'json'

example_json = '{ "age": 1, "name": "Tommy Pickles" }'

JSON.parse(example_json) #=> {"age"=>1, "name"=>"Tommy Pickles"}

# If we want to have symbols for keys instead of strings
JSON.parse(example_json, symbolize_names: true) #=> {:age=>1, :name=>"Tommy Pickles"}

JSON in the real world

List of JSON APIs

MBTA API

MBTA API Intro guide Get stops near a specific lat/long:

http://realtime.mbta.com/developer/api/v2/stopsbylocation?api_key=wX9NwuHnZU2ToO7GmGR9uw&lat=42.346961&lon=-71.076640&format=json

Response:

{
  "stop": [
    {
      "distance": "0.0535630360245705",
      "parent_station": "place-bbsta",
      "parent_station_name": "Back Bay",
      "stop_id": "11384",
      "stop_lat": "42.34735",
      "stop_lon": "-71.075727",
      "stop_name": "Dartmouth St @ Back Bay Sta"
    },
    {
      "distance": "0.0535630360245705",
      "parent_station": "place-bbsta",
      "parent_station_name": "Back Bay",
      "stop_id": "23391",
      "stop_lat": "42.34735",
      "stop_lon": "-71.075727",
      "stop_name": "Back Bay Station"
    },
    {
      "distance": "0.0535630360245705",
      "parent_station": "place-bbsta",
      "parent_station_name": "Back Bay",
      "stop_id": "176",
      "stop_lat": "42.34735",
      "stop_lon": "-71.075727",
      "stop_name": "Dartmouth St opp Back Bay Sta"
    },
    {
      "distance": "0.0535630360245705",
      "parent_station": "",
      "parent_station_name": "",
      "stop_id": "place-bbsta",
      "stop_lat": "42.34735",
      "stop_lon": "-71.075727",
      "stop_name": "Back Bay"
    },
    {
      "distance": "0.0535630360245705",
      "parent_station": "place-bbsta",
      "parent_station_name": "Back Bay",
      "stop_id": "70014",
      "stop_lat": "42.34735",
      "stop_lon": "-71.075727",
      "stop_name": "Back Bay - Outbound"
    },
    {
      "distance": "0.0535630360245705",
      "parent_station": "place-bbsta",
      "parent_station_name": "Back Bay",
      "stop_id": "70015",
      "stop_lat": "42.34735",
      "stop_lon": "-71.075727",
      "stop_name": "Back Bay - Inbound"
    },
    {
      "distance": "0.072804681956768",
      "parent_station": "place-bbsta",
      "parent_station_name": "Back Bay",
      "stop_id": "Back Bay",
      "stop_lat": "42.347487",
      "stop_lon": "-71.075399",
      "stop_name": "Back Bay"
    },
    {
      "distance": "0.0910642221570015",
      "parent_station": "",
      "parent_station_name": "",
      "stop_id": "71855",
      "stop_lat": "42.348245",
      "stop_lon": "-71.076218",
      "stop_name": "Stuart St @ Dartmouth St"
    },
    {
      "distance": "0.150986462831497",
      "parent_station": "",
      "parent_station_name": "",
      "stop_id": "1395",
      "stop_lat": "42.345156",
      "stop_lon": "-71.074969",
      "stop_name": "Dartmouth St @ Appleton St"
    },
    {
      "distance": "0.164772421121597",
      "parent_station": "",
      "parent_station_name": "",
      "stop_id": "1384",
      "stop_lat": "42.345018",
      "stop_lon": "-71.074771",
      "stop_name": "Dartmouth St @ Appleton St"
    },
    {
      "distance": "0.167072579264641",
      "parent_station": "",
      "parent_station_name": "",
      "stop_id": "178",
      "stop_lat": "42.349373",
      "stop_lon": "-71.076911",
      "stop_name": "Saint James Ave @ Dartmouth St"
    },
    {
      "distance": "0.176442056894302",
      "parent_station": "",
      "parent_station_name": "",
      "stop_id": "179",
      "stop_lat": "42.347595",
      "stop_lon": "-71.079984",
      "stop_name": "Ring Rd @ Huntington Ave"
    },
    {
      "distance": "0.212157785892487",
      "parent_station": "place-coecl",
      "parent_station_name": "Copley",
      "stop_id": "70154",
      "stop_lat": "42.349974",
      "stop_lon": "-71.077447",
      "stop_name": "Copley - Inbound"
    },
    {
      "distance": "0.212157785892487",
      "parent_station": "place-coecl",
      "parent_station_name": "Copley",
      "stop_id": "175",
      "stop_lat": "42.349974",
      "stop_lon": "-71.077447",
      "stop_name": "Boylston St @ Dartmouth St"
    },
    {
      "distance": "0.212157785892487",
      "parent_station": "",
      "parent_station_name": "",
      "stop_id": "place-coecl",
      "stop_lat": "42.349974",
      "stop_lon": "-71.077447",
      "stop_name": "Copley"
    }
  ]
}