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up vote 2 down vote favorite

I know theres tutorials on this around the place but I'm having real troubles with this one.

I want to break down a json string into a bunch of smaller objects. I basicaly have 2 servers. One acting as the webapp interface to the whole application and the other is a repository/database.

I'm able to pull down information from the repo to the web app in a json string but after that I don't know how to turn it back.

Heres a sample of the json coming back. 

{"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"}},

Basically there are 4 tags in the json.

page website elementType elementData

I would like to do something like create 4 arrays and populate them with the object that matches these tags but havent the first inkling as to how to do it.

I would imaging its 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

Desired output as requested by apneadiving

The desired output is to have 4 arrays each containing different types of objects. Eg 

  @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.

So how do i turn Json back to objects in ruby and reference them (something like tag name?)?

P.s In the JSON there is already a tag title respPages and respWebsites which is basically all the objects grouped.

share|improve this question
 
I don't understand: you want the json string to be transformed into an object? If so: ActiveSupport::JSON.decode(string) –  apneadiving Aug 10 '11 at 15:17
 
Not quite. I want to identify objects within the json string. The string is multiple objects combined, not singular –  OVERTONE Aug 10 '11 at 15:19
 
give a detailed example of your expected output –  apneadiving Aug 10 '11 at 15:21
 
@apeneadiving. 4 arrays full of objects as determined by the json string is the short answer. Edited question –  OVERTONE Aug 10 '11 at 15:26
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2 Answers

up vote 3 down vote accepted

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 { }.

share|improve this answer
 
The key part is the bit im having trouble with. I don't know how to compare a specific part of the json with a plain string. Javascript short would by document.getElementById() or get by xpath. Is there any way to compare it? p.s thanks for the note on the arrays –  OVERTONE Aug 10 '11 at 15:29
 
@OVERTONE: "thanks" is generally traduced with +1 on stackoverflow :) –  apneadiving Aug 10 '11 at 15:44
 
Ok so theres just 2 parts to this i don't understand. @data would have to be an array or hash for it to use the .each method. But I have no idea how to deserialize the json into one of these. Second is kind of dependent on 1. if theres no way to get data then theres no way to compare the keys. So short recap, how do i turn the JSON into an array or hash that I can cycle through? –  OVERTONE Aug 10 '11 at 15:51
 
@apeneadiving noted –  OVERTONE Aug 10 '11 at 15:56
 
Maybe I'm missing something, but the JSON example you provided has both hashes and arrays in it. There's also something missing, probably because it was truncated. –  tadman Aug 10 '11 at 16:17
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up vote 0 down vote

The following works:

json = {"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"=>nil, "updated_at"=>"2011-08-10T11:00:19Z", "website_url"=>nil, "id"=>1}}, 
        "respElementTypes"=>[{"element_type"=>{"created_at"=>"2011-08-10T11:00:19Z", "updated_at"=>"2011-08-10T11:00:19Z", "id"=>1, "tag_name"=>"head"}}]}

@respPages, @respSite, @respElementTypes = [], [], []

json.each do |key_category, group_category|
  group_category.each do |hash|
    if group_category.is_a? Array
      eval("@#{key_category}") << hash.values.first
    elsif group_category.is_a? Hash
      eval("@#{key_category}") << hash[1]
    end
  end
end

there weren't any respData in your sample but you've got the idea.

share|improve this answer
 
doesn't it precisely answer? –  apneadiving Aug 10 '11 at 17:13
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