Add the action to get Book by a BookId.

lib/decentralised_book_index/metadata.ex

@@ -30,6 +30,7 @@ defmodule DecentralisedBookIndex.Metadata do
 
       define :list_books, action: :read
       define :get_book_by_id, args: [:id], action: :by_id
+      define :get_book_by_bid, args: [:type, :bid], action: :by_bid
       define :get_book_alternative_editions, args: [:book], action: :get_alternative_editions
       define :get_author_books, args: [:author], action: :get_author_books
       define :update_book, action: :update

lib/decentralised_book_index/metadata/book.ex

@@ -69,6 +69,13 @@ defmodule DecentralisedBookIndex.Metadata.Book do
       filter expr(id == ^arg(:id))
     end
 
+    read :by_bid do
+      argument :type, :string, allow_nil?: false
+      argument :bid, :string, allow_nil?: false
+      get? true
+      filter expr(exists(bids, type == ^arg(:type) and bid == ^arg(:bid)))
+    end
+
     read :get_alternative_editions do
       argument :book, :struct, allow_nil?: false