Unable to use dot syntax for ruby hash

Question

I'm using net/http to pull in some json data from the Yahoo Placemaker API. After receiving the response I am performing JSON.parse on the response. This gives me a hash that looks like:

{"processingTime"=>"0.001493", "version"=>"1.4.0.526 build 111113", "documentLength"=>"25", "document"=>{"administrativeScope"=>{"woeId"=>"2503863", "type"=>"Town", "name"=>"Tampa, FL, US", "centroid"=>{"latitude"=>"27.9465", "longitude"=>"-82.4593"}}, "geographicScope"=>{"woeId"=>"2503863", "type"=>"Town", "name"=>"Tampa, FL, US", "centroid"=>{"latitude"=>"27.9465", "longitude"=>"-82.4593"}}, "localScopes"=>{"localScope"=>{"woeId"=>"2503863", "type"=>"Town", "name"=>"Tampa, FL, US (Town)", "centroid"=>{"latitude"=>"27.9465", "longitude"=>"-82.4593"}, "southWest"=>{"latitude"=>"27.8132", "longitude"=>"-82.6489"}, "northEast"=>{"latitude"=>"28.1714", "longitude"=>"-82.2539"}, "ancestors"=>[{"ancestor"=>{"woeId"=>"12587831", "type"=>"County", "name"=>"Hillsborough"}}, {"ancestor"=>{"woeId"=>"2347568", "type"=>"State", "name"=>"Florida"}}, {"ancestor"=>{"woeId"=>"23424977", "type"=>"Country", "name"=>"United States"}}]}}, "extents"=>{"center"=>{"latitude"=>"27.9465", "longitude"=>"-82.4593"}, "southWest"=>{"latitude"=>"27.8132", "longitude"=>"-82.6489"}, "northEast"=>{"latitude"=>"28.1714", "longitude"=>"-82.2539"}}, "placeDetails"=>{"placeId"=>"1", "place"=>{"woeId"=>"2503863", "type"=>"Town", "name"=>"Tampa, FL, US", "centroid"=>{"latitude"=>"27.9465", "longitude"=>"-82.4593"}}, "placeReferenceIds"=>"1", "matchType"=>"0", "weight"=>"1", "confidence"=>"8"}, "referenceList"=>{"reference"=>{"woeIds"=>"2503863", "placeReferenceId"=>"1", "placeIds"=>"1", "start"=>"15", "end"=>"20", "isPlaintextMarker"=>"1", "text"=>"Tampa", "type"=>"plaintext", "xpath"=>""}}}}

I am able to access elements by doing things like jsonResponse['version'] but I am not able to do jsonResponse.version. Why is this?

I don't think Ruby supports that. – Rishav Rastogi Feb 20 '12 at 05:58 — Rishav Rastogi, Feb 20 '12 at 05:58

score 116 · Accepted Answer · edited Jan 14 '19 at 20:24

116

Hash does not have dot-syntax for it's keys. OpenStruct does:

require 'ostruct'
hash = {:name => 'John'}
os = OpenStruct.new(hash)
p os.name #=> "John"

NOTE: Does not work with nested hashes.

edited Jan 14 '19 at 20:24

Joshua Pinter

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answered Feb 20 '12 at 07:24

steenslag

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1

Only for one level of dots os.name.firstname does not seem to work, os.name returns a normal hash – teknopaul Dec 14 '16 at 12:47
1

This does not work for nested hashes and arrays. See whodabudda's answer below. – B Seven Dec 25 '17 at 14:36

score 50 · Answer 2 · answered Mar 24 '17 at 18:17

OpenStruct will work well for a pure hash, but for hashes with embeded arrays or other hashes, the dot syntax will choke. I came across this solution, which works well without loading in another gem: https://coderwall.com/p/74rajw/convert-a-complex-nested-hash-to-an-object basic steps are:

data = YAML::load(File.open("your yaml file"))
json_data = data.to_json
mystr = JSON.parse(json_data,object_class: OpenStruct)

you can now access all objects in mystr using dot syntax.

"Since both JSON and OpenStruct are in the Ruby Standard Library, we'll have no third-party dependencies." — Eduardo Santana, Dec 03 '17 at 14:38

steel · Answer 3 · 2018-12-10T15:42:24.180

17

Ruby hashes don't work like this natively, but the HashDot gem would work for this.

HashDot allows dot notation syntax use on hashes. It also works on json strings that have been re-parsed with JSON.parse.

require 'hash_dot'

hash = {b: {c: {d: 1}}}.to_dot
hash.b.c.d => 1

json_hash = JSON.parse(hash.to_json)
json_hash.b.c.d => 1

edited Dec 10 '18 at 15:42

answered Jun 14 '15 at 22:38

steel

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Nice gem! Thanks! – Richard Aug 02 '17 at 15:37

vinibrsl · Answer 4 · 2018-08-08T14:44:40.303

If you don't want to install any gems, you can try to use the Ruby's native Struct class and some Ruby tricks, like the splat operator.

# regular hashes
customer = { name: "Maria", age: 21, country: "Brazil" }
customer.name
# => NoMethodError: undefined method `name' for {:name=>"Maria", :age=>21, :country=>"Brazil"}:Hash

# converting a hash to a struct
customer_on_steroids = Struct.new(*customer.keys).new(*customer.values)
customer_on_steroids.name
#=> "Maria"

Please note that this simple solution works only for single-level hashes. To make it dynamic and fully functional for any kind of Hash, you'll have to make it recursive to create substructs inside your struct.

You can also store the Struct as if it was a class.

customer_1 = { name: "Maria", age: 21, country: "Brazil" }
customer_2 = { name: "João",  age: 32, country: "Brazil" }
customer_3 = { name: "José",  age: 43, country: "Brazil" }

Customer = Struct.new(*customer_1.keys)
customer_on_steroids_1 = Customer.new(*customer_1.values)
customer_on_steroids_2 = Customer.new(*customer_2.values) 
customer_on_steroids_3 = Customer.new(*customer_3.values)

Read more about Ruby Struct class.

I was looking for an analog to C#'s anonymous type and this works great. — ZX9, Apr 22 '22 at 16:19

score 9 · Answer 5 · answered Feb 20 '12 at 06:45

9

Why not, you can do this via metaprogramming

module LookLikeJSON
  def method_missing(meth, *args, &block)
    if has_key?(meth.to_s)
      self[meth.to_s]
    else
      raise NoMethodError, 'undefined method #{meth} for #{self}' 
    end
  end
end

h = {"processingTime"=>"0.001493", "version"=>"1.4.0.526 build 111113", "documentLength"=>"25"}
h.extend(LookLikeJSON)
h.processingTime #=> "0.001493"

answered Feb 20 '12 at 06:45

megas

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interpolate string in single quote? : / And using `stringify_keys!` to normalize the keys first. – Yuanfei Zhu Mar 06 '12 at 04:49
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Perhaps a smaller, single-line version of this: `Hash.define_method(:method_missing) { |*args| m = args.first; fetch(m, nil) || fetch(m.to_s, nil) || super(*args) }` – Henry Blyth Mar 23 '21 at 18:07

score 6 · Answer 6 · answered Feb 20 '12 at 05:57

6

That is a JavaScript feature, not a Ruby feature. In Ruby, to use a "dot syntax", the object would need to respond to those methods. Ruby hashes use the #[](key) method to access elements.

answered Feb 20 '12 at 05:57

d11wtq

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score 3 · Answer 7 · answered Nov 17 '21 at 20:14

I'm gonna go ahead and piggyback off @whodabudda with this one liner

# example hash
hash = { some: [ {very: :deep}, {very: :nested}, {very: :hash} ] }

#one-liner to convert deep open
deep_open = JSON.parse(hash.to_json, object_class: OpenStruct)

#now you can do this sorcery!
deep_open.some.map(&:very)
=> ["deep", "nested", "hash"]

score 0 · Answer 8 · answered Aug 21 '18 at 07:26

0

If it's in Rspec stubs will work too.

let(:item) { stub(current: 1, total: 1) }

answered Aug 21 '18 at 07:26

Eddie

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Salvatore Mendola · Answer 9 · 2022-08-05T23:43:21.773

If round-tripping JSON seems like too much overhead:

# Constructor like OpenStruct, but not open; and deep, not shallow
# Example: hash = { a: 1, b: { c: 2, d: 3 } }
#          obj = DeepStruct.new(hash)
#          obj.a # read
#          obj.b.c += 1 # read and write 
#          obj.x # error
class DeepStruct
  def initialize(hash)
    hash.each do |k, v|
      self.class.send(:attr_accessor, k)
      instance_variable_set("@#{k}", v.is_a?(Hash) ? DeepStruct.new(v) : v)
    end
  end
end

score -1 · Answer 10 · answered Feb 20 '12 at 10:25

-1

Because Hash doesn't have a version method.

answered Feb 20 '12 at 10:25

Jörg W Mittag

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Unable to use dot syntax for ruby hash

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