Create your first diary app with Ruby on Rails

Created by Piotr Szotkowski (chastell) and Tomasz Stachewicz (tomash)

We will create a little voting app from scratch using a web development framework for Ruby called Rails. Think what your first application should be about – ideally something simple that includes a collection of some sort: e.g., a to-do list, a diary, etc. We’ll use a diary as the base here.

COACH: For the rationale behind this slightly different beginners tutorial, take a look at this post.

Make sure you have Rails installed. Follow the installation guide to get set up.

Get to know the tools


Text Editor

  • Atom, Sublime Text, Vim and Emacs are examples of text editors your can use for writing code and editing files.


Terminal (known as Command Prompt on Windows)

  • Where you start the rails server and run commands.


Web browser

  • (Firefox, Safari, Chrome) for viewing your application.

COACH: Assist with the installation; make sure the text editor is set up properly (e.g., check whether the encoding is UTF-8).


It is important that you select the instructions specific to your operating system - the commands you need to run on a Windows computer are slightly different to Mac or Linux. If you’re having trouble check the Operating System switcher at the bottom of the commands. In case you’re using a cloud service (e.g. nitrous), you need to run the Linux commands even if you are on a Windows computer.


File and folder

Create a new directory (folder) and create a file named index.html in it. Open that file in your editor and web browser.

COACH: Explain that browsers can open local files, only the URL looks stranger than usual.

HTML skeleton

Start by adding a general skeleton for your HTML by writing the below into the index.html file:

<!doctype html>
    <title>My Little Webapp: Coding Is Magic</title>
    <meta charset="UTF-8" />
    <link rel="stylesheet" href="" />

COACH: Explain the two main parts of HTML, <head> and <body>. Explain the <title> tag and (briefly) <meta> , <link> and <script> if needed. Bootstrap is there so that CSS can be skipped altogether (unless participants want to cover it).

First visible content

Add the following HTML between the <body> and </body> tags (feel free to adjust the contents…):

<h1>My Rails Girls Diary</h1>
    <h2>Submitted a Rails Girls application</h2>
      <p>Just submitted an application to a Rails Girls workshop. Can’t wait to see whether I’ll get in!</p>
      <h2>Got in!</h2>
      <p>Received an email that my application got accepted! I’ll be at a RG workshop next week!</p>
    <h2>The first day starts…</h2>
      <p>Today is the first day of the Rails Girls workshop. My coach is quite strange but it seems we all have Rails installed now and can start learning.</p>

These are your first three diary entries. Note how the different tags get displayed and note the recurring structure.

COACH: Tell a bit about HTML tags and their semantic meaning.


Add the following either before or after the above diary entries (again, do adjust to taste):

  <h1>My favourite websites</h1>
      <li><a href="">Rails Girls</a></li>
      <li><a href="">Wikibooks</a></li>
      <li><a href="">Ruby on Rails Guides</a></li>
  <img src="" />

This is an HTML unordered list with some list items containing anchors (links) with hypertext references (URLs) to other pages. It’s followed by a paragraph containing an image – and the image’s source is at the given URL.

COACH: Explain how the Web works and talk a bit about HTML elements and attributes.

Here’s a link to repo with styled basic app you can use.

Moving to Rails

COACH: If your students are on Windows, consider using Nitrous.IO as the basis for the following parts.

New Rails application

Open a terminal window (Command Prompt on Windows), change to the directory where your files are (using the cd command) and run rails new diary – this will take some time and end up creating a new Rails application. Run cd diary to change to the app’s directory.

COACH: Explain how to navigate directories and run commands.

Running the server

Once in the diary directory run rails server and (once it finishes starting up) go to http://localhost:3000 in your browser. You should see the ‘Welcome aboard’ page. Stop the server by pressing ctrl-c.

COACH: Explain what has happened and what’s the output in the terminal window. If the server fails to start due to a missing JavaScript runtime, gem install therubyracer and uncomment the relevant line in Gemfile.

First route and view

Create the controller and the route

Run rails generate controller welcome index – this will generate your first controller and a route that leads to it. Start your server and go to http://localhost:3000 to see that your application indeed does support the /welcome/index route.

Stop the server and run rake routes to see all the routes supported by your application.

COACH: Explain URLs and the URL hierarchy. Explain how in Rails URLs map to ‘what happens behind the scene’.

Move the view to be the top of your site

Edit the config/routes.rb file and uncomment (remove the # from the front) the root ’welcome#index’ line (this will probably be the 7th line). This will make the root of your application be the view rendered by the Welcome#index action. Go to http://localhost:3000 and see that indeed the main page of your application now serves this view (rather than the ‘Welcome aboard’ page).

COACH: Explain how the main page of an application is the root of the URL hierarchy and that it’s the page that people visit when they just put the host name into the browser’s address bar.

Move the existing HTML to the right view

Edit the app/views/welcome/index.html.erb file and copy the contents of the <body> tags from your original index.html file (i.e., the list of diary entries and the website links) there, replacing the two lines (with <h1> and <p>) in the view. Refresh the browser to see that the page now indeed contains the right contents.

COACH: Explain that the view only contains the part between <body> and </body>, as the rest is common to the whole application and is defined elsewhere.


Repeated content

If you look at the structure of your list of links, it seems that every list item looks similar to the others – it contains a URL (where the link should take the user when clicked) and a name (what should the user see and be able to click on). Rather than writing the links as raw HTML (and potentially make a mistake with some of them) let’s abstract this a bit and iterate over a collection of URL-and-name pairs.

Replace the contents of the <ul> tags with the following:

  @websites = [
    ["", "Rails Girls"],
    ["", "Wikibooks"],
    ["", "Ruby on Rails Guides"],
<% for url, name in @websites %>
  <li><a href="<%= url %>"><%= name %></a></li>
<% end %>

Refresh the browser window to see whether your page still has the same links.

COACH: Explain what happened – what is an array, what do <% and <%= ERb tags mean (and how they differ), how iteration works.

Keeping code or data (like the above @websites array) in views is simple, but a bad practice and can bite in the long run. For starters let’s move the @websites array from the view to the controller. Remove it from the view and put it in app/controllers/welcome_controller.rb in the index method so it looks like this:

class WelcomeController < ApplicationController
  def index
    @websites = [
      ["", "Rails Girls"],
      ["", "Wikibooks"],
      ["", "Ruby on Rails Guides"],

Note that after refreshing your browser window nothing should change – this is because variables starting with @ (called ‘instance variables’) can be accessed by both the view and the controller.

COACH: Explain the connection between the WecomeController#index action and the view; note and emphasise the difference between @-starting @websites and plain url or name.

Create the model

With the website links out of the hard-coded way, let’s do something with the diary entries. This time we won’t (ab)use a simple Ruby structure like an array, but a proper model that represents a given entry’s data. Let’s start with generating the model – run rails generate model Entry title:string date:date contents:text to create an Entry model that can represent a diary entry with a title, a publication date and some contents.

COACH: Explain what models are and the field:type notation for generating them; explain the difference between string and text types if necessary.

Migrate the database

Run rails db:migrate to migrate the database so that its structure contains a table for entries.

COACH: Explain what databases are (in abstract terms, as vessels for storing our application’s data and providing model structures) and why they are needed. Explain that things which are in memory won’t get persisted by default and they need to be persisted explicitly to be available on the next request.

Play with the model in the Rails console

Now that we have a model, we can start creating instances of that model – i.e., actual diary entries that aren’t hard-coded in the HTML view. For this, we’ll learn a new tool: the Rails console. Start it with rails console and, once it boots and shows: you the >> prompt, create a few entries:

>> Entry.create "title" => "Submitted a Rails Girls application", "date" =>, 2, 1), "contents" => "Just submitted an application to a Rails Girls workshop. Can’t wait to see whether I’ll get in!">> Entry.create "title" => "Got in!", "date" =>, 2, 15), "contents" => "Received an email that my application got accepted! I’ll be at a RG workshop next week!">> Entry.create "title" => "The first day starts…", "date" =>, 2, 22), "contents" => "Today is the first day of the Rails Girls workshop. My coach is quite strange but it seems we all have Rails installed now and can start learning."

Note how the console – just like rails server – shows you a log of what happens in the background. You can always get an array of all existing entries via Entry.all.

COACH: Explain what’s going on. Slowly.

Viewing the persisted contents

Add the model instances to the existing view

Edit the WelcomeController#index action (in the app/controllers/welcome_controller.rb file) and add the following either before or after the lines containing @websites definition:

@entries = Entry.all

Edit the app/views/welcome/index.html.erb view and replace the lines with the diary entries with the following:

<% for entry in @entries %>
  <h2><%= entry.title %></h2>
    <p><%= %></p>
    <p><%= entry.contents %></p>
<% end %>

COACH: Discuss what happened; discuss what’s the order of the entries and how they can be reordered (say, by reverse date) and where it should happen.

Create a controller for diary entries

Now that we have a model we need to create a controller for handling actions related to the instances of the model (creating new entries, showing, editing and deleting existing ones). Run rails generate controller Entries – this should generate the EntriesController class. Check rake routes – notice that the controller isn’t enough, we still need to point URLs to the controller’s actions.

Edit config/routes.rb and add a resources "entries" line somewhere inside the Diary::Application.routes.draw block. Run rake routes again: notice how now your application has all kinds of new routes.

COACH: Explain how Rails’ route resources work and how they make URLs spring to existence and map to controller actions by default.

A view of all the entries

As can be seen in the rake routes output, the URLs are wired to their relative controller actions. Let’s see what’s missing – visit http://localhost:3000/entries in your browser. Uh-oh, it seems like the ‘index’ action is missing – let’s add it – open app/controllers/entries_controller.rb and add the below empty method inside the class definition:

def index

Now refresh the browser – we no longer have an ‘unknown action’ problem, we now have a ‘template is missing’ problem. Save an empty file as app/views/entries/index.html.erb (note it’s just like the index.html.erb file in the ‘welcome’ directory before, but this time it’s in the ‘entries’ directory) and refresh the browser again – it should display an empty page. This is good, as our view is quite empty at the moment.

COACH: Explain how actions render the related views by default.

Now go to the app/controllers/welcome_controller.rb file and find the WelcomeController#index method (the one that starts with def index). Find the line that sets the @entries variable (it should start with @entries =) and copy it to EntriesController#index (so to the index method of the EntriesController, which can be found in app/controllers/entries_controller.rb). Similarly, go to the app/views/welcome/index.html.erb view and copy the @entries.each block (all of the indented lines up to and including the matching end) to the app/views/entries/index.html.erb view. Refresh the browser: it should now show the list of all your diary entries.

COACH: Explain that even though this might look like little to no progress, there is a significant change: we’re no longer operating in the context of the main page of our app, but rather a list of diary entries only (without the links to other websites, for example).

A view of a single entry

Note how, when you run rake routes, the output says that the /entries/:id(.:format) pattern maps to the entries#show controller action. Go to http://localhost:3000/entries/1 – the URL for your first diary entry; notice how we’re, again, missing an action of the EntriesController. Add that (empty for now) action, then refresh the browser and add the (likewise, empty) missing view.

COACH: Guide through adding the missing action and view if needed; make sure the process (all the way from deciphering the right rake routes line) is well understood.

Now, let’s figure out how to interpret the 1 from the end of the URL to display the right entry. Make the EntriesController#show action look like this:

def show
  @entry = Entry.find(params["id"])

This line means ‘take the id parameter and use it in the Entry.find method to find the right entry’. Now edit the app/views/entries/show.html.erb view and put there the following:

<h2><%= @entry.title %></h2>
  <p><%= %></p>
  <p><%= @entry.contents %></p>

Visit http://localhost:3000/entries/1 and compare it with http://localhost:3000/entries/2 to see how using params[’id’] means that different diary entries get displayed.

COACH: Explain that the :id part of the URL template from rake routes is made into a key for the params hash; discuss what else can be found in the params hash.

Linking entries

Run rake routes again; notice how the row for the entries#show action starts with entry in the ‘prefix’ column. Go to the app/views/entries/index.html.erb view and change the line responsible for displaying the title to the below:

<h2><%= link_to(entry.title, entry_path(entry)) %></h2>

Note how we use the link_to method that takes two parameters, the text to display (entry.title) and the path to link to. Check the source of the page to see what is the path for subsequent titles. Note how the path is created by calling the entry_path method with entry as its argument.

COACH: Remind how the HTML for links looks like. Explain the relation between entry_path and the entry prefix from rake routes. Explain why the entry_path method needs the entry argument. Explain what the entry_url method does (and how it differs from the entry_path method) if you want to.

Now let’s try to get back from an entry screen to the index of all entries: edit the app/views/entries/show.html.erb template and add a link to the entries index, like this:

<p><%= link_to("Back to all entries", entries_path) %></p>

Note, again, how the entries prefix from rake routes is used to construct the entries_path method name. Note how this method does not need a parameter.

Creating entries via the UI

Adding the ‘new entry’ form

Now that we have a way to display a list of all entries and a single entry, let’s add a way to create new diary entries. Run rake routes and try to figure out which URL (and action) is responsible for new entry creation.

Go to the index of all entries and add a link for creating new entry:

<%= link_to("New entry", new_entry_path) %>

Click the link – and add the missing action and view.

COACH: Make sure this process is well understood by now.

Edit the app/views/entries/new.html.erb view and paste in the below:

<%= form_for( do |form| %>
  <p><%= form.label("title") %></p>
  <p><%= form.text_field("title") %></p>
  <p><%= form.label("contents") %></p>
  <p><%= form.text_area("contents") %></p>
  <p><%= form.submit %></p>
<% end %>
<p><%= link_to("Back to all entries", entries_path) %></p>

Note: we can skip labels for now

COACH: Show how the HTML produced by the form_for helper looks like and try to explain how it works.

Handling the ‘new entry’ form

Refresh the browser and try adding a new entry – you should see the well-known-by-now ‘unknown action’ error. Add the action to the EntriesController, but for starters let’s display what the action receives:

def create
  render(:text => params.inspect)

Refresh the browser and inspect what exactly the action gets as its params.

COACH: Explain how filling a text field and a text area and submitting the form ends up with all the params being POSTed to the controller’s action. Explain what .inspect does.

Creating and persisting the new entry

Edit the create action and make it look like this:

def create
  entry_params = params["entry"]
  entry = Entry.create(entry_params)

Note how we try to get the parameters of the new entry (its title and contents) from the params hash and then create a new entry from them, just like in the console. Try submitting the form again – notice that we’re still not there yet, as we get a ActiveModel::ForbiddenAttributesError.

This error is because of security measures – it’s relatively simple to POST whatever parameters a user wants to, and Rails protects us from a rogue user that would want to set parameters that they’re not supposed to set (like ‘id’). We need to declare which parameters can be set by the user; change the first line of the create action to the below:

entry_params = params["entry"].permit("title", "contents")

Now try submitting the form again – this time it should work and you should get redirected to the newly-created entry.

COACH: Make sure the plucking of the new entry’s parameters from params is well understood and that it’s accepted that certain fields need to be permitted explicitly. Editing via the UI

Adding the ‘edit entry’ form

Now that we can view and create entries, let’s also add the option to edit them. Run rake routes and try to guess which route is responsible for editing an entry.

COACH: Make sure this is well understood by now.

Edit the app/views/entries/show.html.erb view and add the below line somewhere:

<p><%= link_to("Edit this entry", edit_entry_path(@entry)) %></p>

Refresh a given entry’s view and click the link. Add the missing action and an empty view.

COACH: Again, make sure this is well understood.

Let’s first make sure our edit action exposes the right entry to the view. Make sure the edit action looks just like the show action – i.e., it grabs the right entry based on the id from the URL:

def edit
  @entry = Entry.find(params["id"])

Now copy the contents of the app/views/entries/new.html.erb view to the app/views/entries/edit.html.erb view, but change the first line so that it’s a form for this particular entry – and, optionally, add a link back to this entry’s show screen:

<%= form_for(@entry) do |form| %>
  <p><%= form.label("title") %></p>
  <p><%= form.text_field("title") %></p>
  <p><%= form.label("contents") %></p>
  <p><%= form.text_area("contents") %></p>
  <p><%= form.submit %></p>
<% end %>
<p><%= link_to("Back to this entry", entry_path(@entry)) %></p>
<p><%= link_to("Back to all entries", entries_path) %></p>

COACH: Make sure all of this is well understood.

Now try to submit the form – which action is still missing? Create it in the controller:

def update
  entry_params = params["entry"].permit("title", "contents")
  entry = Entry.find(params["id"])

Check whether this all works and whether you can now edit the entries.

COACH: Make sure the update action’s contents are well understood – from permitting params through finding entries to redirecting to the right path.

Further ideas

Play with your application! Here are some further ideas you might want to add: