Return Struct as JSON

I am working on a side project in which I want to use Sinatra as a simple backend and experiment with a more rich Javascript front end.

The Setup

The idea was to respond to a GET request to my endpoint with a JSON-ified array of simple Ruby Structs.

The route looked something like

get '/api/v1/tracks' do
  track_lister = TackLister.new
  track_lister.tracks.to_json
end

the call to the TrackLister's tracks was to return an array of Track structs.

class TrackLister
  Track = Struct.new(:name, :artist)

  def tracks
    [].tap do |tracks|
      2.times { |i| tracks << Track.new("Track #{i}", "Band #{i}") }
    end
  end
end

firing up irb this seems to have worked well enough

>> TrackLister.new.tracks
#=> [
  #<struct TrackLister::Track name="Track 0", artist="Band 0">,
  #<struct TrackLister::Track name="Track 1", artist="Band 1">
]

The Problem

The to_json version of my response looks a little funny

>> require 'json' #=> true
>> TrackLister.new.tracks.to_json
#=> "[\"#<struct TrackLister::Track name=\\\"Track 0\\\", artist=\\\"Band 0\\\">\",\"#<struct TrackLister::Track name=\\\"Track 1\\\", artist=\\\"Band 1\\\">\"]"

Since this was supposed to be a response Javascript would need to parse I figured I would check to see how Javascript would handle it:

>> JSON.parse(my_long_json_string)
=> [
  "#<struct TrackLister::Track name="Track 0", artist="Band 0">",
  "#<struct TrackLister::Track name="Track 1", artist="Band 1">"
]

It can parse the JSON but it results in an array of strings and there seemed to be no easy way for me to get to the data

>> tracks[0]
=> "#<struct TrackLister::Track name="Track 0", artist="Band 0">"
>> tracks[0]['name']
=> undefined
>> tracks[0].name
=> undefined
>> JSON.parse(tracks[0])
=> Uncaught SyntaxError: Unexpected identifier

It seemed that the JSON version of my structs was not being deserialized the way I would have liked.

The Solution

The solution was to serialize my data in a way that Javascript would like and could easily deserialize - a Hash.

With the addition of to_h in Ruby 2 converting my Track struct into a Hash was very easy:

>> TrackLister.new.tracks.map(&:to_h)
#=> [{:name=>"Track 0", :artist=>"Band 0"}, {:name=>"Track 1", :artist=>"Band 1"}]

this could then be converted to JSON just like before

>> TrackLister.new.tracks.map(&:to_h).to_json
#=> "[{\"name\":\"Track 0\",\"artist\":\"Band 0\"},{\"name\":\"Track 1\",\"artist\":\"Band 1\"}]"

Now when test out this new JSON string in Javascript's JSON.parse I end up with Javascript objects

>> tracks = JSON.parse(my_long_json_string)
=> [Object, Object]

which allow me to easily access my data's attributes

>> tracks[0]
=> Object {name: "Track 0", artist: "Band 0"}
>> tracks[0].name
=> "Track 0"
>> tracks[0].artist
=> "Band 0"