fetch json file then manipulate data with ruby

Question

I am using ruby version 2.0.0, I have a demo.json file which looks like this:

{ "demo": 
  { 
    "rama" : { "Name": "demo" },
    "krishna" : { "Name": "hare","place": "bharat", "hawa": { "maina": "tota"} } 
  }
}

Now I try to manipulate json file by this way:

require 'json'
options = {}
options[:demo] = "kailash"
 File.open("demo.json","w") do |f|

    f.write(JSON.pretty_generate(options))

end

I want to replace some values and to add some new key-value pairs in the existing JSON file and don't wants to completely replace the entire JSON file. Is there any way to do this?

You need to use JSON::parse method, to get the hash object first. Then iterate though the hash, and update the value whatever you want. When done, use Hash#to_json method to make it a JSON object and then write it back to the file. — Arup Rakshit
– Arup Rakshit, Commented Mar 30, 2014 at 11:46
sure tell me what value you want to update in your .json file ? — Arup Rakshit
– Arup Rakshit, Commented Mar 30, 2014 at 12:09

Uri Agassi · Accepted Answer · 2014-03-30 13:27:06Z

6

You must first read and parse your file, then make your changes, and finally you can overwrite the file with the updated object:

require 'json'

options = JSON.parse(IO.read('demo.json'))
options['demo']['kailash'] = { "Name" => "new" }

File.open("demo.json","w") do |f|

    f.write(JSON.pretty_generate(options))

end

Output file:

{
  "demo": {
    "rama": {
      "Name": "demo"
    },
    "krishna": {
      "Name": "hare",
      "place": "bharat",
      "hawa": {
        "main": "tota"
      }
    },
    "kailash": {
      "Name": "new"
    }
  }
}

edited Mar 30, 2014 at 13:27

answered Mar 30, 2014 at 12:56

Uri Agassi

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4 Comments

Arup Rakshit Over a year ago

+1.. Yes this is the way to solve it, as I said in the comment.

Daniël Knippers Over a year ago

A slightly shorter way to write is File.write('demo.json', JSON.pretty_generate(options))

Pradeep Gupta Over a year ago

But what if i wants to update value of existing key like "rama" ?

Uri Agassi Over a year ago

options['demo']['rama']['new_key'] = ['new_value']

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