Ruby JSON parse changes Hash keys

Question

Lets say I have this Hash:

{
  :info => [
    {
        :from => "Ryan Bates",
        :message => "sup bra",
        :time => "04:35 AM"
    }
  ]
}

I can call the info array by doing hash[:info].

Now when I turn this into JSON (JSON.generate), and then parse it (JSON.parse), I get this hash:

{
  "info" => [
    {
        "from" => "Ryan Bates",
        "message" => "sup bra",
        "time" => "04:35 AM"
    }
  ]
}

Now if I use hash[:info] it returns nil, but not if I use hash["info"].

Why is this? And is there anyway to fix this incompatibility (besides using string keys from the start)?

wyattisimo · Accepted Answer · 2014-02-25 19:23:08Z

167

The JSON generator converts symbols to strings because JSON does not support symbols. Since JSON keys are all strings, parsing a JSON document will produce a Ruby hash with string keys by default.

You can tell the parser to use symbols instead of strings by using the symbolize_names option.

Example:

original_hash = {:info => [{:from => "Ryan Bates", :message => "sup bra", :time => "04:35 AM"}]}
serialized = JSON.generate(original_hash)
new_hash = JSON.parse(serialized, {:symbolize_names => true})

new_hash[:info]
 #=> [{:from=>"Ryan Bates", :message=>"sup bra", :time=>"04:35 AM"}]

Reference: http://www.ruby-doc.org/stdlib-1.9.3/libdoc/json/rdoc/JSON.html#method-i-parse

edited Feb 25, 2014 at 19:23

answered Aug 20, 2012 at 6:51

wyattisimo

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2 Comments

Boushley Over a year ago

And I think it's :symbolize_keys now (rubydoc.info/gems/multi_json/1.3.2/MultiJson)

wyattisimo Over a year ago

@Boushley: No, it's still symbolize_names. My answer references the JSON engine that ships with the Ruby standard library. You're referencing a third-party gem.

Community · Accepted Answer · 2017-05-23 12:26:07Z

25

In short, no. Think about it this way, storing symbols in JSON is the same as storing strings in JSON. So you cannot possibly distinguish between the two when it comes to parsing the JSON string. You can of course convert the string keys back into symbols, or in fact even build a class to interact with JSON which does this automagically, but I would recommend just using strings.

But, just for the sake of it, here are the answers to this question the previous times it's been asked:

what is the best way to convert a json formatted key value pair to ruby hash with symbol as key?

ActiveSupport::JSON decode hash losing symbols

Or perhaps a HashWithIndifferentAccess

edited May 23, 2017 at 12:26

CommunityBot

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answered Sep 25, 2011 at 5:42

Lee Jarvis

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1 Comment

LanguagesNamedAfterCofee Over a year ago

Thanks for the links, but like you said, I'll just use strings for the keys

aaron.v · Accepted Answer · 2015-03-13 22:16:44Z

7

I solved my similar issue with calling the with_indifferent_access method on it

Here I have a json string and we can assign it to variable s

s = "{\"foo\":{\"bar\":\"cool\"}}"

So now I can parse the data with the JSON class and assign it to h

h = JSON.parse(s).with_indifferent_access

This will produce a hash that can accept a string or a symbol as the key

h[:foo]["bar"]
  #=> "cool"

answered Mar 13, 2015 at 22:16

aaron.v

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2 Comments

Mark Over a year ago

Is with_indifferent_access added to Hash via something in the Rails ecosystem?

aaron.v Over a year ago

@Mark you are correct. Here is a link api.rubyonrails.org/v4.2.5/classes/ActiveSupport/…

Jdfreefly · Accepted Answer · 2014-01-15 20:54:16Z

3

Use ActiveSupport::JSON.decode, it will allow you to swap json parsers easier
Use ActiveSupport::JSON.decode(my_json, symbolize_names: true)

This will recursively symbolize all keys in the hash.

(confirmed on ruby 2.0)

answered Jan 15, 2014 at 20:54

Jdfreefly

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1 Comment

nruth Over a year ago

seems to be removed in rails 4.1? edgeguides.rubyonrails.org/… and api.rubyonrails.org/classes/ActiveSupport/JSON.html states option support removed

Graham · Accepted Answer · 2017-09-27 17:05:19Z

2

It's possible to modify all the keys in a hash to convert them from a string to a symbol:

symbol_hash = Hash[obj.map{ |k,v| [k.to_sym, v] }]

puts symbol_hash[:info]
# => {"from"=>"Ryan Bates", "message"=>"sup bra", "time"=>"04:35 AM"}

Unfortunately that doesn't work for the hash nested inside the array. You can, however, write a little recursive method that converts all hash keys:

def symbolize_keys(obj)
  #puts obj.class # Useful for debugging
  return obj.collect { |a| symbolize_keys(a) } if obj.is_a?(Array)
  return obj unless obj.is_a?(Hash)
  return Hash[obj.map{ |k,v| [k.to_sym, symbolize_keys(v)] }]
end

symbol_hash = symbolize_keys(hash)
puts symbol_hash[:info]
# => {:from=>"Ryan Bates", :message=>"sup bra", :time=>"04:35 AM"}

edited Sep 27, 2017 at 17:05

Graham

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answered May 5, 2017 at 6:29

Kathryn

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Comments

Community · Accepted Answer · 2020-04-05 00:07:35Z

1

You can't use that option like this

ActiveSupport::JSON.decode(str_json, symbolize_names: true)

In Rails 4.1 or later, ActiveSupport::JSON.decode no longer accepts an options hash for MultiJSON. MultiJSON reached its end of life and has been removed.

You can use symbolize_keys to handle it. Warning: It works only for JSON strings parsed to hash.

ActiveSupport::JSON.decode(str_json).symbolize_keys

edited Apr 5, 2020 at 0:07

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answered May 4, 2017 at 3:04

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