collection of persistence helper methods

helper_methods.ex

defmodule FunctionHead do
  def create(attrs) when is_map(attrs) do
    with {:ok, doc} <- new(attrs),
         {:ok, _ } <- persist(doc),
     do: {:ok, doc}
  end
  def persist(doc), do: ExAws.Dynamo.put_item(__MODULE__.table_name, doc)

  def where(filter) when is_map(filter) do
     with {:ok, response } <- ExAws.Dynamo.get_item(__MODULE__.table_name, filter),
                              decoded = decode(response),
     do: new(decoded)
  end

  def new(attrs)
  def new(attrs: nil), do: {:ok, nil}
  def new(attrs) when is_map(attrs) do
        with doc <- doc_struct(attrs),
             IO.puts("doc: #{ inspect(doc) }"),
             {:ok, mdoc} <- migrate(doc),
         do: {:ok, doc_struct(mdoc)}
  end

  defp doc_struct(doc)
  defp doc_struct(doc: nil), do: nil
  defp doc_struct(doc) when is_map(doc), do: struct(__MODULE__, doc)

  defp decode(doc) when is_map(doc) do
    if Map.has_key?(doc, "Item"), do: (ExAws.Dynamo.Decoder.decode(doc["Item"], as: __MODULE__))
  end

  def migrate(doc), do: doc

end

[dev@localhost function_head]$ iex -S mix
Erlang/OTP 18 [erts-7.2] [source-e6dd627] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false]

lib/function_head.ex:18: warning: this clause cannot match because a previous clause at line 18 always matches
Compiled lib/function_head.ex
Interactive Elixir (1.2.0) - press Ctrl+C to exit (type h() ENTER for help)