How do I parse JSON with Ruby on Rails?

I'm looking for a simple way to parse JSON, extract a value and write it into a database in Rails.

Specifically what I'm looking for, is a way to extract shortUrl from the JSON returned from the bit.ly API:

{
  "errorCode": 0,
  "errorMessage": "",
  "results":
  {
    "http://www.foo.com":
    {
       "hash": "e5TEd",
       "shortKeywordUrl": "",
       "shortUrl": "http://bit.ly/1a0p8G",
       "userHash": "1a0p8G"
    }
  },
  "statusCode": "OK"
}

And then take that shortUrl and write it into an ActiveRecord object associated with the long URL.

This is one of those things that I can think through entirely in concept and when I sit down to execute I realize I've got a lot to learn.

These answers are a bit dated. Therefore I give you:

hash = JSON.parse string

Rails should automagically load the json module for you, so you don't need to add require 'json'.

Parsing JSON in Rails is quite straightforward:

parsed_json = ActiveSupport::JSON.decode(your_json_string)

Let's suppose, the object you want to associate the shortUrl with is a Site object, which has two attributes - short_url and long_url. Than, to get the shortUrl and associate it with the appropriate Site object, you can do something like:

parsed_json["results"].each do |longUrl, convertedUrl|
  site = Site.find_by_long_url(longUrl)
  site.short_url = convertedUrl["shortUrl"]
  site.save
end

This answer is quite old. pguardiario's got it.

One site to check out is JSON implementation for Ruby. This site offers a gem you can install for a much faster C extension variant.

With the benchmarks given their documentation page they claim that it is 21.500x faster than ActiveSupport::JSON.decode

The code would be the same as Milan Novota's answer with this gem, but the parsing would just be:

parsed_json = JSON(your_json_string)

Here is an update for 2013.

Ruby

Ruby 1.9 has a default JSON gem with C extensions. You can use it with

require 'json'
JSON.parse ''{ "x": "y" }'
# => {"x"=>"y"}

The parse! variant can be used for safe sources. There are also other gems, which may be faster than the default implementation. Please refer to multi_json for the list.

Rails

Modern versions of Rails use multi_json, a gem that automatically uses the fastest JSON gem available. Thus, the recommended way is to use

object = ActiveSupport::JSON.decode json_string

Please refer to ActiveSupport::JSON for more information. In particular, the important line in the method source is

data = MultiJson.load(json, options)

Then in your Gemfile, include the gems you want to use. For example,

group :production do
  gem 'oj'
end

This can be done as below, just need to use JSON.parse, then you can traverse through it normally with indices.

#ideally not really needed, but in case if JSON.parse is not identifiable in your module  
require 'json'

#Assuming data from bitly api is stored in json_data here

json_data = '{
  "errorCode": 0,
  "errorMessage": "",
  "results":
  {
    "http://www.foo.com":
    {
       "hash": "e5TEd",
       "shortKeywordUrl": "",
       "shortUrl": "http://whateverurl",
       "userHash": "1a0p8G"
    }
  },
  "statusCode": "OK"
}'

final_data = JSON.parse(json_data)
puts final_data["results"]["http://www.foo.com"]["shortUrl"]

Ruby's bundled JSON is capable of exhibiting a bit of magic on its own.

If you have a string containing JSON serialized data that you want to parse:

JSON[string_to_parse]

JSON will look at the parameter, see it's a String and try decoding it.

Similarly, if you have a hash or array you want serialized, use:

JSON[array_of_values]

Or:

JSON[hash_of_values]

And JSON will serialize it. You can also use the to_json method if you want to avoid the visual similarity of the [] method.

Here are some examples:

hash_of_values = {'foo' => 1, 'bar' => 2}
array_of_values = [hash_of_values]

JSON[hash_of_values] 
# => "{\"foo\":1,\"bar\":2}"

JSON[array_of_values] 
# => "[{\"foo\":1,\"bar\":2}]"

string_to_parse = array_of_values.to_json
JSON[string_to_parse]
# => [{"foo"=>1, "bar"=>2}]

If you root around in JSON you might notice it's a subset of YAML, and, actually the YAML parser is what's handling JSON. You can do this too:

require 'yaml'

YAML.load(string_to_parse)
# => [{"foo"=>1, "bar"=>2}]

If your app is parsing both YAML and JSON, you can let YAML handle both flavors of serialized data.

require 'json'
out=JSON.parse(input)

This will return a Hash

require 'json'

hash = JSON.parse string

work with the hash and do what you want to do.

RUBY is case sensitive.

require 'json' # json must be lower case

JSON.parse(<json object>)  

for example

JSON.parse(response.body) # JSON must be all upper-case

The Oj gem (https://github.com/ohler55/oj) should work. It's simple and fast.

http://www.ohler.com/oj/#Simple_JSON_Writing_and_Parsing_Example

require 'oj'

h = { 'one' => 1, 'array' => [ true, false ] }
json = Oj.dump(h)

# json =
# {
#   "one":1,
#   "array":[
#     true,
#     false
#   ]
# }

h2 = Oj.load(json)
puts "Same? #{h == h2}"
# true

The Oj gem won't work for JRuby. For JRuby this (https://github.com/ralfstx/minimal-json) or this (https://github.com/clojure/data.json) may be good options.

Here's what I would do:

json = "{\"errorCode\":0,\"errorMessage\":\"\",\"results\":{\"http://www.foo.com\":{\"hash\":\"e5TEd\",\"shortKeywordUrl\":\"\",\"shortUrl\":\"http://b.i.t.ly/1a0p8G\",\"userHash\":\"1a0p8G\"}},\"statusCode\":\"OK\"}"

hash = JSON.parse(json)
results = hash[:results]

If you know the source url then you can use:

source_url = "http://www.foo.com".to_sym

results.fetch(source_url)[:shortUrl]
=> "http://b.i.t.ly/1a0p8G"

If you don't know the key for the source url you can do the following:

results.fetch(results.keys[0])[:shortUrl]
=> "http://b.i.t.ly/1a0p8G"

If you're not wanting to lookup keys using symbols, you can convert the keys in the hash to strings:

results = json[:results].stringify_keys

results.fetch(results.keys[0])["shortUrl"]
=> "http://b.i.t.ly/1a0p8G"

If you're concerned the JSON structure might change you could build a simple JSON Schema and validate the JSON before attempting to access keys. This would provide a guard.

NOTE: Had to mangle the bit.ly url because of posting rules.

You can try something like this:

def details_to_json
{
  :id                    => self.id, 
  :credit_period_type    => self.credit_period_type,
  :credit_payment_period => self.credit_payment_period,

 }.to_json
end