Handle bad JSON gracefully with Hash#fetch

问题:

I'm trying to fetch some products from this JSON API so I can display them in my views, with bad JSON gracefully handled using Hash#fetch to declare a default value if I get nil.

But why am I getting:

can't convert String into Integer

or if I set @json_text to {}:

undefined method 'fetch' for `nil:NilClass`

Live app: http://runnable.com/U-QEWAnEtDZTdI_g/gracefully-handle-bad-json

class MainController < ApplicationController
  require 'hashie'

  def index
    @json_text = <<END
{
    "products": []
}
END

    hashes = JSON.parse(@json_text)
    mashes = Hashie::Mash.new(hashes)

    products = []

    mashes.products.fetch('products', []).each do |mash|
      puts "YOLO"
    end
  end
end

回答1:

The right way to fetch is by calling fetch on mashes variable:

mashes.fetch('products', []).each do |mash|
  puts "YOLO"
end

#fetch is a Hash method and in this case is the same as mashes['product'], except when product is nil, using the fetch example will return []