 
   """
   def list_articles do
-    Repo.all(Article)
+    Article
+    |> Repo.all()
+    |> Repo.preload(author: [user: :credential])
   end
 
   @doc """

      ** (Ecto.NoResultsError)

  """
  def get_author!(id), do: Repo.get!(Author, id)

  @doc """
  Creates a author.

      ** (Ecto.NoResultsError)

  """
  def get_article!(id) do
    Article
    |> Repo.get!(id)
    |> Repo.preload(author: [user: :credential])
  end

  @doc """
  Creates a article.
