How to avoid "undefined method `[]' for nil:NilClass" when working with nested Ruby hashes?

Question

I'm working with the Steam Storefront API - http://store.steampowered.com/api/appdetails/?appids=240

I've parsed the JSON into a hash.

When I try to select any hash value nested inside of "data" I receive an "undefined method `[]' for nil:NilClass" error.

I can puts the whole lot with res["240"]["data"] which shows me all of the keys and values. All of which seem to look fine.

However when I try to go one branch further it throws nil.

res["240"]["data"]["type"]

Using .key also throws up an error.

res["240"]["data"].key

My quest to find an answer has mainly found suggestions of searching for the key & values, however I know the direct route to the data so I'd like to go this route if possible.

Thanks.

paradox460 · Accepted Answer · 2016-01-12 03:02:51Z

5

If you're on ruby 2.3, you may use dig, as suggested by @sawa.

http://docs.ruby-lang.org/en/2.3.0/Hash.html#method-i-dig

However, if you are not on ruby 2.3, then things get a bit trickier.

The simplest approach is to implement your own version of dig:

class Hash
  def dig(*path)
    path.inject(self) do |h, k|
      h.respond_to?(:keys) ? h[k] : nil
    end
  end
end

Then you can just res.dig("240", "data", "type")

answered Jan 12, 2016 at 3:02

paradox460

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1 Comment

grim Over a year ago

@sawa answer works, however thank you for taking into consideration I might not have had 2.3 yet. It's rather lucky they released "dig" just before I needed it :)

cdmo · Accepted Answer · 2020-02-11 14:11:50Z

4

You can use dig in combination with the safe navigation operator, like:

res&.dig("240", "data", "type")

If res is nil (or more accurately isn't "digable") then it will return nil instead of raising.

answered Feb 11, 2020 at 14:11

cdmo

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Comments

sawa · Accepted Answer · 2016-01-12 01:06:09Z

1

Use dig.

res.dig("240", "data", "type")

answered Jan 12, 2016 at 1:06

sawa

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4 Comments

tomsabin Over a year ago

nil does not implement .dig: [3] pry(main)> nil.dig("240", "data", "type") NoMethodError: undefined method 'dig' for nil:NilClass

sawa Over a year ago

@tomsabin So what? How is that relevant to the question?

tomsabin Over a year ago

My misunderstanding of the question - thinking that res was originally nil.

sawa Over a year ago

Quote from the question: "I've parsed the JSON into a hash."

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