Dynamic database configuration in Phoenix

.env

[default]
DB_NAME=mydb
DB_PASSWORD=mypass
DB_USERNAME=myuser

repo.ex

defmodule MyApp.Repo do
  use Ecto.Repo,
    otp_app: :my_app,
    adapter: Ecto.Adapters.Postgres

  @doc """
    In the production mode you cannot run ConfigParser.parse_file(".env") or Mix.env()
    So to detect the environment mode put a flag to config/prod.exs:
       config :my_app, MyApp.Repo, env: :prod
  """
  def init(_, config) do
    if config[:env] == :prod do
      {:ok, config}
    else
      {:ok, inject_env(config)}
    end
  end

  defp inject_env(config) do
    config
    |> Enum.map(fn item ->
      case ConfigParser.parse_file(".env") do
        {:ok, %{"default" => conf}} -> modify_config(conf, item)
        _ -> item
      end
    end)
  end

  defp modify_config(conf, item) do
    case item do
      {:username, nil} -> {:username, conf["DB_USERNAME"]}
      {:password, nil} -> {:password, conf["DB_PASSWORD"]}
      {:database, nil} -> {:database, conf["DB_NAME"]}
      _ -> item
    end

  end
end