Update to make Author has many AuthorRoles.

lib/decentralised_book_index/metadata/author.ex

@@ -115,8 +115,6 @@ defmodule DecentralisedBookIndex.Metadata.Author do
       attribute_writable? true
     end
 
-    belongs_to :author_role, Metadata.AuthorRole do
-      attribute_writable? true
-    end
+    has_many :author_role, Metadata.AuthorRole
   end
 end

lib/decentralised_book_index/metadata/author_role.ex

@@ -42,8 +42,8 @@ defmodule DecentralisedBookIndex.Metadata.AuthorRole do
       allow_nil? true
     end
 
-    has_one :author, Metadata.Author do
-      allow_nil? false
+    belongs_to :author, Metadata.Author do
+      allow_nil? true
     end
   end
 end