The url shortener Elixir app

Published October 19, 2018 by Toran Billups

So far my Elixir journey has focused more on independent features of the language and less about real app construction. The next 15/20 days will be a bit different because I'm now ready to apply everything I've learned in hopes of going deeper. With each iteration I'll be adding something new or improving some functionality from a previous post.

The application itself will be simple and much less the focus of this series as you might imagine. The url shortener has a small api surface area and offers enough (primitive) "real world" requirements that it should make for a great learning playground.

Part 1: mix new

The first step is to run `mix new` from the command line. This will scaffold everything we need to kickstart a simple project in Elixir.

    mix new example

Before we dive into building the web interface or anything to make this concurrent I first wanted to write the most basic module required. Start by adding a module called `Shortener`. In this module we will first implement a function called `create_short_url` that is responsible for inserting the url and hash (alias). Next implement a function called `get_url` that is responsible for retrieving the url given some hash (alias).

    defmodule Shortener do
      def new(), do: %{}
      def create_short_url(state, hash, url) do
        Map.put(state, hash, url)
      def get_url(state, hash) do
        Map.get(state, hash, :undefined)

To see this in action we next write a unit test to exercise the 2 functions together. You can run this from the command line using `mix test`.

    defmodule ShortenerTest do
      use ExUnit.Case, async: true
      setup do
      test "create will add key/value given url and hash", state do
        assert Shortener.get_url(state, "x") === :undefined
        new_state = Shortener.create_short_url(state, "x", "")
        assert Shortener.get_url(new_state, "x") === ""

Note: the state returned from `setup` is made available to each unit test as `state` just before the `do`

To play around with this module in IEx run this command `iex -S mix run`

    state =
    new_state = Shortener.create_short_url(state, "x", "")
    Shortener.get_url(new_state, "x")

You can track my progress on github commit by commit. If you just want the code for this post checkout this commit.

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