You'll want to talk to the API and the best way to do this is using the Shopify API gem. Add the following to your Gemfile
gem 'shopify_api'
gem 'rest-client'
Then bundle.
In order to get started you are going to need to setup your application as a Private Application on your shop. To do this, create a new private application:
https://YOURSHOP.myshopify.com/admin/apps/private/new
Once created, go to the application and find the API keys, add them to your .env:
SHOPIFY_API_KEY="YOUR_API_KEY"
SHOPIFY_PASSWORD="YOUR_PASSWORD"
SHOPIFY_SHOP="YOUR_SHOP_NAME"
Once you have the API keys in your .env you should import them into your config/secrets.yml:
shopify_api_key: <%= ENV["SHOPIFY_API_KEY"] %>
shopify_password: <%= ENV["SHOPIFY_PASSWORD"] %>
shopify_shop: <%= ENV["SHOPIFY_SHOP"] %>
Once you've setup your API keys you'll want to preload them in an initializer. Create /config/initializers/shopify.rb:
shopify_shop_url = "https://#{Rails.application.secrets.shopify_api_key}:#{Rails.application.secrets.shopify_password}@#{Rails.application.secrets.shopify_shop}.myshopify.com/admin"
ShopifyAPI::Base.site = shopify_shop_url
product.add_metafield(ShopifyAPI::Metafield.new({ :description => 'Author of book', :namespace => 'book', :key => 'author', :value => 'Kurt Vonnegut', :value_type => 'string' }))