Using Sinatra to Parse JSON data from url - ruby

Question

I'm using Sinatrarb to complete a task
I need to:
Parse the data of a JSON object from a url,
Single out one of attributes of the json data and store it as a variable
Run some arithmetic on the variable
Return the result as a new variable
then post this to a new url as a new json object.
I have seen bits and pieces of information all over including information on parsing JSON data in ruby and information on open-uri but I believe it would be very valuable having someone break this down step by step as most similar solutions given to this are either outdated or steeply complex.
Thanks in advance.

Answer 1

Here's a simple guide. I've done the same task recently.
Let's use this JSON (put it in a file called 'simple.json'):
{
"name": "obscurite",
"favorites": {
"icecream": [
"chocolate",
"pistachio"
],
"cars": [
"ferrari",
"porsche",
"lamborghini"
]
},
"location": "NYC",
"age": 100}
Parse the data of a JSON object from a url.
Step 1 is to add support for JSON parsing:
require 'json'
Step 2 is to load in the JSON data from our new .json file:
json_file = File.read('simple.json')
json_data = JSON.parse(json_file)
Single out one of attributes of the json data and store it as a variable
Our data is in the form of a Hash on the outside (curly braces with key:values). Some of the values are also hashes ('favorites' and 'cars'). The values of those inner hashes are lists (Arrays in Ruby). So what we have is a hash of hashes, where some hashes are arrays.
Let's pull out my location:
puts json_data['location'] # NYC
That was easy. It was just a top level key/value. Let's go deeper and pull out my favorite icecream(s):
puts json_data['favorites']['icecream'] # chocolate pistachio
Now only my second favorite car:
puts json_data['favorites']['cars'][1] # porsche
Run some arithmetic on the variable
Step 3. Let's get my age and cut it down by 50 years. Being 100 is tough!
new_age = json_data['age'] / 2
puts new_age
Return the result as a new variable
Step 4. Let's put the new age back into the json
json_data['age'] = new_age
puts json_data['age'] # 50
then post this to a new url as a new json object.
Step 5. Add the ability for your program to do an HTTP POST. Add this up at top:
require 'net/http'
and then you can post anywhere you want. I found a fake web service you could use, if you just want to make sure the request got there.
# use this guy's fake web service page as a test. handy!
uri = URI.parse("http://jsonplaceholder.typicode.com/posts")
header = {'Content-Type'=> 'text/json'}
http = Net::HTTP.new(uri.host, uri.port)
request = Net::HTTP::Post.new(uri.request_uri, header)
request.body = json_data.to_json
response = http.request(request)
# Did we get something back?
puts response.body
On linux or mac you can open a localhost port and listen as a test:
nc -4 -k -l -v localhost 1234
To POST to this port change the uri to:
uri = URI.parse("http://localhost:1234")
Hope this helps. Let me know if you get stuck and I'll try to lend a hand. I'm not a ruby expert, but wanted to help a fellow explorer. Good luck.