• We'll be working through the creation of the mydiary Rails app, a sample online diary application.
  • I will be working on a CSSE Linux cluster machine.
    • See https://cssegit.monmouth.edu/cshelp/csseremote/-/wikis/MUCSremote for remote access instructions.

• Run these commands in a Terminal.
  • pay attention to the comments marked with “#”

cd work_dir # where work_dir is a directory of your choice

mkdir rails # create rails directory

cd rails

rails new mydiary # This rails command will create a mydiary project directory.

cd mydiary

• All the newly-created directories in the mydiary directory will make up the mydiary rails web app.
  • app: Contains most of the Ruby source code and output templates directly associated with the app; most directly connected to the MVC components of the Web app.
    • app/controllers: Contains the controller files
    • app/helpers: Contains ruby source code files that provide methods that you can use from views
    • app/views: Contains output templates (views) for the app.
  • config: Contains configuration files for the app.
  • db: Used for database dumps, backups and migrations. In the case of apps that use SQLite, contains the database file(s).
  • bin: Contains important scripts and command line tools used in constructing and deploying Rails apps.

• The Gemfile in mydiary belongs to bundler, which manages Ruby gems dependencies for your new rails project.
  • Gemfile can be customized in a text editor if needed to add custom gem dependencies to your project.

• See config/database.yml
  • database.yml is a YAML file with info about the database(s) that the app will use.
  • Note “development,” “test” and “production” targets.

• The Rails scaffolding mechanism generates default, generic code to provide a full set of basic Web app operations for any of your models.
  • These “Web app operations” are the CRUD (Create, Retrieve, Update, and Delete) operations and views on any database table
  • You can then build your own views and controller methods off of this basic scaffolding.
  • Run the following command in the Terminal:

rails generate scaffold Entry title:string content:text

• For our mydiary application, entries will initially solely consist of a title and some content.
• There are other attributes (or “fields” in the database sense) that Rails will add by default to the underlying database table, such as id (a unique numeric identifier).
• A directive is also added into the default migration (database creation) code to create timestamp columns: created_at (a timestamp of when the record/associated object was created), and updated_at (a timestamp of when the record/associated object was amended last).
• Because of this automation, it is only necessary to specify the two custom, additional attributes to the scaffold generator to get things going.

• We're building an online diary.
• Our model is the diary entry that we'll call Entry.
• The scaffolding step above defined our database table and its fields to reflect the structure of our model.
• In Rails, models and database tables generally have a direct relationship.
  • If you have a database table called entries, then this will be directly related to a model class in your Rails app called Entry.
  • Rails naming conventions
    • expects objects from a singular class name to be saved to a database table which is the plural of the class name
      • Example: expects objects from the class Person to be saved to a database table named people (not “persons”)
        • Rails has a pluralization engine to figure out what object maps to what table.

• Database tables can be created directly with SQL or other db frontend if desired.
  • But the preferred way is to use migrations.
    • Migrations are mostly database independent and allow you to manage changes to your db's schema over time and give you the ability to “roll back” to older versions of your schema.
    • See the migration script that was automatically generated by the previous generate scaffold command. It will be a .rb script found in db/migrate that looks something like this:

class CreateEntries < ActiveRecord::Migration
  def change
	create_table :entries do |t|
	  t.string :title
	  t.text :content

	  t.timestamps null: false
	end
  end
end

• By default, table names are pluralized and model names are singular.
  • Example: table name entries & model name Entry
  • Rails works out the difference between singular and plural names automatically.

• Use the Rails rake command to create the database tables using a migration.
  • rake tasks are administrative tasks associated with your app that are managed by the rake tool.
    • This tool is analogous to the make command used for C/C++ development.
    • Notice the Rakefile in the root of your app directory structure.
  • After running the following rake command, you should notice a SQLite database file development.sqlite3 in the db project directory.

### Recommended in rails 4+ (bundle forces use of the rake version specified in Gemfile) ###
bundle exec rake db:migrate

• Per https://www.fngtps.com/2019/rails6-blocked-host
• Edit the config/environments/development.rb file and add the following code somewhere inside the Rails.application.configure do block:

# Authorize access from any host:
config.hosts.clear

rails server -b 0.0.0.0 -p <port>
   ### If on a Linux cluster machine, <port> = some value > 3000 ###

• Running the above rails server… command should start a simple development web server to serve your app.
  • Start a web browser on the same host that the rails server is running on, and browse the URL and port that the web server provides.
    • For example, if simple web server output includes “0.0.0.0:3010”, browse the rails app using the URL http://localhost:3010
  • Also try browsing the subpage that corresponds with the controller that was created by the Scaffolding step:
    • See app/controllers
    • e.g., http://localhost:3010/entries

• The default “route” for a new Rails application is just a generic Rails web page that is displayed.
  • The generic Rails page is generated by the 'root route' of your mydiary app.
    • To replace this page, we'll set up a different root route later.
  • To begin using the entries controller, you must browse the following 'route':

          http://localhost:<your chosen port>/entries

• As you browse your app, the simple web server that you are running your rails app on will be throwing output in the Terminal window in which you started it.
  • The output includes SQL queries that are used to extract needed information from the app's sqlite3 db.

• This part describes what the scaffolding step generated, how it works, and how it can be extended with custom methods and views.

• Controller actions
  • Within the app's directory structure, see app/controllers/entries_controller.rb, which contains a class definition for the Entries controller and its methods.
    • Rails controllers are implemented as classes that inherit from more generic ApplicationController and ActionController classes.
    • The index, new and create methods all make calls to methods of the Entry class, such as Entry.new and Entry.all.
      • Entry is the model class, which inherits methods from the generic ActiveRecord class that allow navigating and finding data in the database table for the Entry model.
        • For example, Entry.find(:all) returns all records as an array of objects from the entries database table.

• The views associated with some controller methods are located in app/views/entries.
  • The .erb files in app/views/entries are HTML template files containing Embedded Ruby.
    • These files define the views of a Rails web app.
    • Embedded Ruby code sections are delimited by <% and %>
    • The following is found in app/views/entries/show.html.erb:

<p id="notice"><%= notice %></p>

<p>
  <strong>Title:</strong>
  <%= @entry.title %>
</p>

<p>
  <strong>Content:</strong>
  <%= @entry.content %>
</p>

<%= link_to 'Edit', edit_entry_path(@entry) %> |
<%= link_to 'Back', entries_path %>

• ERB files may contain different forms of the <% tag. The differences between them are explained at https://stackoverflow.com/questions/7996695/what-is-the-difference-between-and-in-erb-in-rails

• Try adding a new method manually to the Entries controller (in app/controllers/entries_controller.rb):

# Defines a new method and, therefore, a new controller action.
# Similar to index, but sorted in descending (DESC) order
# by creation time.
# GET /entries/view_all
def view_all
    @entries = Entry.order('created_at DESC').all
end

• If we want to use this new controller method, it is necessary to tell the Rails routing system (the system that sends incoming request to the correct controllers and methods) that you have defined a new method that may be called on the entries controller.
  • We need to edit the config/routes.rb file, and add some statements just BEFORE the following line (2nd line of file):

resources :entries

• The statements to add are:

# Redefining root route as the view_all action:
root 'entries#view_all'

# Defining this route to use new view_all controller action:
get '/entries/view_all' => 'entries#view_all'

• After that, attempting to use the new view_all method at http://localhost:<your port>/entries/view_all should result in an error message in the browser window stating something like “Template is missing … Missing template …”
  • This means that the associated view for view_all still needs to be created in app/views/entries.
    • Edit a new file app/views/entries/view_all.html.erb.
    • Put the following Embedded Ruby code in view_all.html.erb, and then try using the view_all action again in the web browser:

<%# view_all.html.erb: Define the view for the view_all controller action. %>
<% @entries.each do |entry| %>
    <h1><%= entry.title %></h1>
    <p><%= entry.content %></p>
    <p><em>Posted at <%= entry.created_at %></em></p>
<% end %>

<%= link_to 'Add New entry', :controller => 'entries', :action => 'new' %>

• See the current mydiary app routes by running the following rake command in a Terminal:

rake routes

• Retry the view_all controller method by visiting http://localhost:<your port>/entries/view_all.

• Try the new root route for your app at http://localhost:<your port>.

• Try adding a “View all entries” link to the show view (app/views/entries/show.html.erb).