Question

I want to break down a JSON string into smaller objects. I have two servers, one acting as the web-app interface to the whole application and the other is a repository/database.

I’m able to retrieve information from the repository to the web-app as JSON, but after that I don’t know how to return it.

Here’s a sample of the JSON being returned:

{"respPages":[{"page":{"page_url":"http://www.google.com/","created_at":"2011-08-10T11:00:19Z","website_id":1,"updated_at":"2011-08-10T11:00:19Z","id":1}},{"page":{"page_url":"http://www.blank.com/services/content_services/","created_at":"2011-08-10T11:02:46Z","website_id":1,"updated_at":"2011-08-10T11:02:46Z","id":2}}],"respSite":{"website":{"created_at":"2011-08-10T11:00:19Z","website_id":null,"updated_at":"2011-08-10T11:00:19Z","website_url":null,"id":1}},"respElementTypes":[{"element_type":{"created_at":"2011-08-10T11:00:19Z","updated_at":"2011-08-10T11:00:19Z","id":1,"tag_name":"head"}},

There are four tags in the JSON:

page
website
elementType
elementData

I would like to create four arrays and populate them with the object that matches these tags.

I would image the code is something like this:

#Get the json from repo using net/http
 uri = URI.parse("http://127.0.0.1:3007/repository/infoid/1.json")
 http = Net::HTTP.new(uri.host, uri.port)
 response = http.request(Net::HTTP::Get.new(uri.request_uri))


@x = response.to_hash

@pages = Array.new
@websites= Array.new
@elementDatas = Array.new
@elementTypes = Array.new

#enter code here`#For every bit of the hash, find out what it is and allocate it accordingly
    @x.each_with_index do |e,index|
    if e.tagName == pages #Getting real javascripty here. There must be someway to check the tag or title of the element
    @pages[index]=e
    end

My goal for the returned value is to have four arrays, each containing different types of objects:

  @pagesArray[1]

should contain the first occurrence of a page object in the JSON string. Then do the same for the other ones.

Of course I’d need to break down the object further but once I can break down the top level and categorize them, then I can go deeper.

In the JSON there are already tag titles respPages and respWebsites which group all the objects.

How do I turn JSON back into objects in Ruby and reference them using something like the tag name?

Answer 1

You should be able to decode anything in JSON format using the standard JSON library:

JSON.load(...)

It will throw exceptions on malformed JSON data, so be sure to test it thoroughly and make sure it can handle all the important cases.

If you’re trying to navigate the structure of the JSON itself, you probably need to write a series of recursive methods that handle each case along the way. A good pattern to start with is this:

@data.each do |key, value|
  case (key)
  when 'someKey'
    handle_some_key(value)
  when 'otherKey'
    handle_other_key(value)
  end
end

You can either break out the behavior into methods as in this example, or inline it if the logic is fairly straightforward.

As a note, an alternative to Array.new is simply [ ] as it is in JavaScript. For example:

@pages = [ ]

You’ll see this used frequently in most Ruby examples. The alternative to Hash.new is { }.