learn-co-students/rack-dynamic-paths-readme-online-web-ft-031119

Dynamic URL Routes

Objectives

1. Explain how dynamic routes prevent web applications from having to be rewritten as new information is added
2. Create dynamic routes

Why Dynamic Routes?

When you create a new repository on GitHub, how do URLs like github.com/jmburges/my-repo get generated? In our current examples, we would have to create a new if statement for each possible URL path. Since this is a dynamic application, our application can't be rewritten every time a new user signs up. So the concept of "dynamic routes" was created.

Setting Up Dynamic Routes

Let's assume we have a playlister app which has an array of Songs. First let's look at our Song object

#song.rb

class Song

  attr_accessor :title, :artist

  def initialize(title, artist)
    @title = title
    @artist = artist
  end

end

Pretty simple class. Now we have our web app.

class Application

  @@songs = [Song.new("Sorry", "Justin Bieber"),
            Song.new("Hello","Adele")]

  def call(env)
    resp = Rack::Response.new
    req = Rack::Request.new(env)
    
    @@songs.each do |song|
      resp.write "#{song.title}\n"
    end

    resp.finish
  end
end

We want more information about each song though. Similarily to GitHub, we want to be able to go to a URL like localhost:9292/songs/Sorry and get all the information on Sorry. We are doing routes like this instead of just plain GET params because it's easier to read. Remember the path is given to us as a string. We could therefore write something like this:

class Application

  @@songs = [Song.new("Sorry", "Justin Bieber"),
            Song.new("Hello","Adele")]

  def call(env)
    resp = Rack::Response.new
    req = Rack::Request.new(env)

    if req.path=="/songs/Sorry"
      resp.write @@songs[0].artist
    elsif req.path == "/songs/Hello"
      resp.write @@songs[1].artist
    end

    resp.finish
  end
end

This is silly though, because every time we create a new Song we would have to create a new if statement. Thankfully, because paths are strings, we can do a regex match against the path. Then we just grab the content after the /song/ to figure out which Song our user would like.

class Application

  @@songs = [Song.new("Sorry", "Justin Bieber"),
            Song.new("Hello","Adele")]

  def call(env)
    resp = Rack::Response.new
    req = Rack::Request.new(env)

    if req.path.match(/songs/)

      song_title = req.path.split("/songs/").last #turn /songs/Sorry into Sorry
      song = @@songs.find{|s| s.title == song_title}

      resp.write song.artist
    end

    resp.finish
  end
end

Now our routes are dynamic! We can just add songs, and everything else is taken care of and works for us. You have written a lot of Ruby; take comfort in your skills.

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