gistfile1.txt

irb(main):021:0> ash = Book.serializable_hash_options
=> {:include=>{:authorships=>{:only=>["id", "author_id", "book_id", "created_at", "updated_at"]}}, :only=>[:id, :title, :created_at, :updated_at, :epub_checksum]}

irb(main):022:0> ash2
=> {:include=>{:spine_items=>{:only=>["id", "author_id", "book_id", "created_at", "updated_at"]}}}

irb(main):023:0> ash.reverse_merge(ash2)
=> {:include=>{:authorships=>{:only=>["id", "author_id", "book_id", "created_at", "updated_at"]}}, :only=>[:id, :title, :created_at, :updated_at, :epub_checksum]}

irb(main):024:0> ash.merge(ash2)
=> {:include=>{:spine_items=>{:only=>["id", "author_id", "book_id", "created_at", "updated_at"]}}, :only=>[:id, :title, :created_at, :updated_at, :epub_checksum]}