Iterating through a ruby nested hash with nils? [duplicate]

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This question already has answers here:

How to avoid NoMethodError for nil elements when accessing nested hashes? [duplicate] (4 answers)

Closed 5 years ago.

Let say I'm getting back a JSON nested hash (or array of hashes) from an API

@example = {"results" = > {{"poop" => "shoop"},{"foo" => {"shizz" => "fizz", "nizzle"=>"bizzle"}}}

YAML markup for the nested hash above

  - poop: shoop
  - foo:
    shizz: fizz
    nizzle: bizzle

Now lets go make a db entry with ActiveRecord from the hash. This works fine.

Thing.create!(:poop  => @example["results"]["poop"],
                :shizz => @example["results"]["foo"]["shizz"],
                :nizzle=> @example["results"]["foo"]["nizzle"])

But what if 'foo' is empty or nil? For example, if an API result has a "person" hash with "first name","last name" # etc, the "person" hash will usually be empty if there is no data, which means the hashes inside it don't exist.

@example = {"results" = > {{"poop" => "shoop"},{"foo" => nil }}

  Thing.create!(:poop  => @example["results"]["poop"],
                :shizz => @example["results"]["foo"]["shizz"],
                :nizzle=> @example["results"]["foo"]["nizzle"])

  NoMethodError: You have a nil object when you didn't expect it! 
  You might have expected an instance of Array. 
  The error occurred while evaluating nil.[]

What's the best way to handle this?

Answer 1

I came accross a nil sensitive Hash#get method a while back.

class Hash
  def get(key, default=nil)
    key.split(".").inject(self){|memo, key_part| memo[key_part] if memo.is_a?(Hash)} || default
  end
end

h = { 'a' => { 'b' => { 'c' => 1 }}}
puts h.get "a.b.c"    #=> 1
puts h.get "a.b.c.d"  #=> nil
puts h.get "not.here" #=> nil

It's pretty handy for this sort of JSON drilling.

Otherwise you have to do stuff like this:

h['a'] && h['a']['b'] && h['a']['b']['c']

And that just sucks.

Answer 2

If you're using rails (not sure if it's in ruby 1.9):

h = {"a"=>1}
h.try(:[],"a") #1
h.try(:[],"b") #nil

h2 = {"c"=>{"d"=>1}}
h2.try(:[],"c").try(:[],"d")   #1
h2.try(:[],"a").try(:[],"foo") #nil

# File activesupport/lib/active_support/core_ext/object/try.rb, line 28
def try(*a, &b)
  if a.empty? && block_given?
    yield self
  else
    __send__(*a, &b)
  end
end

Answer 3

I went ahead and started passing all Hash results into a Hashie Mash. That way they behave like Ruby objects and respond to nils like a champ!

Answer 4

Ruby 2.3.0 introduced a new method called dig on both Hash and Array that solves this problem entirely.

value = hash.dig(:a, :b)

It returns nil if the key is missing at any level.