Rails New and other basics

Generate or Clone an application

Generate a brand new application

cd to the folder where you want to store your new application. For me, this is cd ~/workspace. Then,
rails new my_fancy_app
This creates a subfolder called my_fancy_app and puts all of the boilerplate for a Rails application inside.
For all subsequent commands, you must cd in to the application folder first; e.g. cd my_fancy_app from ~/workspace.

Or if you cloned an existing application

cd in to the folder you just downloaded. Then,
bundle install
The bundle install (or just bundle for short) command fetches all of the 3rd party Ruby code that the application depends upon and installs it on your machine. You only need to do this once per application.

Start the web server

On Cloud9,
rails server -b $IP -p $PORT
or on your own computer
rails server
rails s is short for rails server, like rails c is short for rails console.
If the server started successfully, you should see output like the following. It may take a moment.
=> Booting WEBrick
=> Rails 5.0.2 application starting in development on http://localhost:3000
=> Run `rails server -h` for more startup options
[2017-05-23 06:32:14] INFO WEBrick 1.3.1
[2017-05-23 06:32:14] INFO ruby 2.3.4 (2017-03-30) [x86_64-darwin16]
[2017-05-23 06:32:15] INFO WEBrick::HTTPServer#start: pid=4618 port=3000
and then the cursor should be blinking at the bottom, but not at the end of your usual command prompt. This window is now dedicated to the web server app, and you can't run any other commands in it until you shut down the server.
If you need to run other command line stuff, open up a new window or tab.

If the server failed to start

  1. 1.
    If you got a "address already in use" error, then you must have an old rails server running in another window or tab somewhere. Find it and Ctrl-C (or just close the tab).
  2. 2.
    If you have a syntax error in config/routes.rb, then the server will refuse to even start up. See if the error message complains about a line in that file.

Shut down the web server

Ctrl-C. On Windows, you may be asked whether to terminate the job; say yes.

Start the Rails Console

rails console
or rails c for short.
Rails Console is a superpowered version of IRB, handy for testing snippets of code.

Set up the database

If the application you cloned requires database setup, then
rails db:migrate
will create the tables and columns.
If I provided some starter dummy data for you, then
rails dev:prime
will quickly pre-populate the tables for you, so you don't have to spend an hour in rails console adding rows.


I am getting an error relating to the pg gem when in bundle install

If your bundle install fails with a message about postgres or pgconfig, then
bundle install --without production

I am getting an error relating to ExecJS or TypeError: Object doesn't support this property or method

Go in to the app/assets/javascripts/application.js file and delete the line
//= require_tree .
Refresh the page in Chrome; it should now be okay.
If you are still experiencing an error, try the following also:
  1. 1.
    In Gemfile, delete the line
    gem 'turbolinks'
  2. 2.
    In app/assets/javascripts/application.js, delete the line
    //= require turbolinks
  3. 3.
    bundle install and restart your server.