Checking if records exist with Memento

[marvoh]

I am using memento to wrap Mnesia functionality into my application.

I want to check if a record with a certain id exists and if not perform certain actions.

Documentation says read should return nil when record doesn’t exist. Howerver, the Memento.transation wrapper aborts with a:not_existsexception therefore my application cannot proceed.

Here’s how my function looks like:

def find_conversation(user_id) do
    Memento.transaction! fn ->
      user_id
      |> read
      |> to_conversation
    end
end

defp to_conversation(nil), do: nil
  defp to_conversation(%@store{} = conversation) do
    struct(Conversation, Map.from_struct(conversation))
  end