Hash#fetch is a great way to ensure that a hash key is present. The error message when a key is missing though is rather useless if you don't have immediate access to the object and want to debug why keys are missing, e.g. in the parsed JSON response of an external API. If you'd like a more detailed error message, you can do a Hash#decent_fetch (with the attached code).

some_hash.fetch('missing_key')
# => KeyError: key not found: "missing_key"
 
some_hash.decent_fetch('missing_key')
# => KeyError: Key "missing_key" not found in {"id"=>"96814974590_10152840169159591", "created_time"=>"2014-11-18T20:30:41+0000", "story"=>"Audi Deutschland commented on a photo."}

UI/UX Design by

We make sure that your target audience has the best possible experience with your digital product. You get:

• Design tailored to your audience
• Proven processes customized to your needs
• An expert team of experienced designers

Read more Show archive.org snapshot

You could put this code in an initializer:

# E.g. config/initializers/hash_decent_fetch.rb.rb
Hash.class_eval do

  def decent_fetch(*args, &block)
    fetch(*args, &block)
  rescue KeyError
    key = args.first
    raise KeyError, "Key #{key.inspect} not found in #{self.inspect}"
  end

end

If you are now thinking about monkey-patching Hash#fetch with this code, please do not do that. The implementation is slower than vanilla #fetch. Use #decent_fetch only when applicable, e.g. when consuming APIs.