Add the action to get author's books.

lib/decentralised_book_index/metadata.ex

@@ -22,6 +22,7 @@ defmodule DecentralisedBookIndex.Metadata do
       define :list_books, action: :read
       define :get_book_by_id, args: [:id], action: :by_id
       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
       define :destroy_book, action: :destroy
     end

lib/decentralised_book_index/metadata/book.ex

@@ -76,6 +76,17 @@ defmodule DecentralisedBookIndex.Metadata.Book do
                             and id != ^book.id)
       end
     end
+
+    read :get_author_books do
+      argument :author, :struct, allow_nil?: false
+
+      prepare fn query, context ->
+        author = query.arguments.author
+
+        Metadata.Book
+        |> Ash.Query.filter(expr(exists(author_roles, author_id == ^author.id)))
+      end
+    end
   end
 
   attributes do