sandbox_three.ex

defmodule Phoenix.Ecto.SQL.Sandbox do
  # ...
  def call(conn, sandbox) do
    conn |> fetch_cookies |> allow_sandbox_access(sandbox)
  end

  defp allow_sandbox_access(%{req_cookies: %{@cookie_name => configuration}} = conn, sandbox) do
    [pid_string,repo_string] = configuration |> URI.decode |> String.split("|")

    owner = to_pid(pid_string)
    repo  = String.to_atom(repo_string)

    Ecto.Adapters.SQL.Sandbox.allow(repo, owner, self())

    conn
  end
  defp allow_sandbox_access(conn, _sandbox), do: conn

  defp to_pid(string) do
    string |> String.to_char_list |> :erlang.list_to_pid
  end
end