Avoid encoding/decoding in controller create

not_working_user_controller.ex

def create(conn, %{"user" => u}) do
    user = struct(User, u)
    IO.inspect user
    
    # %App.User{created_at: nil, email: nil}
end

working_user_controller.ex

def create(conn, %{"user" => user}) do
    user = struct(User, JSON.encode!(u) |> JSON.decode!(keys: :atoms!))
    IO.inspect user
    
    # %App.User{created_at: nil, email: "[email protected]"} 
end

defmodule SafeMapToStruct do
  defmacro __using__(_opts) do
    quote do
      @before_compile unquote(__MODULE__)
    end
  end

  defmacro __before_compile__(_env) do
    quote do
      @safed_keys Map.from_struct(%__MODULE__{}) |> Map.keys |> Enum.map(&to_string/1)
      def from_map(map) do
        SafeMapToStruct.from_map(map, __MODULE__, @safed_keys)
      end
    end
  end

  def from_map(map, module, safed_keys) do
    struct(module, for {key, val} <- map, to_string(key) in safed_keys do
      case key do
        k when is_binary(k) -> {String.to_atom(k), val}
        k when is_atom(k)   -> {k, val}
      end
    end)
  end
end

defmodule User do
  use SafeMapToStruct
  defstruct name: nil, age: 123

end