Add an action to get author's alternatives names.

lib/decentralised_book_index/metadata.ex

@@ -10,6 +10,7 @@ defmodule DecentralisedBookIndex.Metadata do
       define :add_author_to_related_alias_registry, action: :add_author_to_related_alias_registry, args: [:name, :description, :related_author_id]
       define :list_authors, action: :read
       define :get_author_by_id, args: [:id], action: :by_id
+      define :get_author_alternative_names, args: [:author], action: :get_alternative_names
       define :update_author, action: :update
       define :destroy_author, action: :destroy
     end

lib/decentralised_book_index/metadata/author.ex

@@ -4,6 +4,8 @@ defmodule DecentralisedBookIndex.Metadata.Author do
     domain: DecentralisedBookIndex.Metadata,
     data_layer: AshPostgres.DataLayer
 
+  require Ash.Query
+
   postgres do
     table "authors"
     repo DecentralisedBookIndex.Repo
@@ -54,6 +56,18 @@ defmodule DecentralisedBookIndex.Metadata.Author do
       get? true
       filter expr(id == ^arg(:id))
     end
+
+    read :get_alternative_names do
+      argument :author, :struct, allow_nil?: false
+
+      prepare fn query, context ->
+        author = query.arguments.author
+
+        DecentralisedBookIndex.Metadata.Author
+        |> Ash.Query.filter(author_alias_registry_id == ^author.author_alias_registry_id
+                            and id != ^author.id)
+      end
+    end
   end
 
   attributes do

test/decentralised_book_index/metadata/author_test.exs

@@ -29,4 +29,22 @@ defmodule DecentralisedBookIndex.Metadata.AuthorTest do
         Metadata.add_author_to_related_alias_registry("Author2", "An description2", nil)
     end
   end
+
+  describe "authors alternatives names" do
+    test "new author has no alternatives names" do
+      {:ok, author} = Metadata.create_author("Author", "An description")
+      assert {:ok, alternatives_names} = Metadata.get_author_alternative_names(author)
+      assert alternatives_names = []
+    end
+
+    test "author has related author so they has one alternative name" do
+      {:ok, related_author} = Metadata.create_author("Author",  "An description")
+
+      {:ok, author} =
+        Metadata.add_author_to_related_alias_registry("Author2", "An description2", related_author.id)
+
+      assert {:ok, alternatives_names} = Metadata.get_author_alternative_names(author)
+      assert alternatives_names = [related_author]
+    end
+  end
 end