Thanks for sharing, this is the working code:
multi_result =
Multi.new()
|> Multi.run(:book_to_be_returned, fn _ -> Works.update_book_to_be_returned_multi(line.book_id) end)
and:
def update_book_to_be_returned_multi(book_id) do
alias Mango.Books
alias Mango.Books.Book
case Repo.get_by(Book, %{id: book_id, status: :out}) do
nil ->
{:error, %{error: "Book not found or already available.."}}
book ->
case Books.update_book(book, %{status: :available}) do
{:ok, book} -> {:ok, book} # update_book returns %{:ok, book_object } so this is the correct match
nil -> {:error, %{error: "Error occured while updating the book.."}}
end
end
end
