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Creating A Migration

Goals

    Topics
    id
    title
    description

    The suggestotron has a list of topics that people can vote on. We'll store our topics in the database. In this step you'll do the following:

  • Create a simple Table in the database for topics with a title and a description

  • Automatically generate the corresponding Scaffold in Rails (namely, the Model, the View, and the Controller).

Steps

Step 1

Type this in the terminal:

Terminal
rails generate scaffold topic title:string description:text
  • generate scaffold tells Rails to create everything necessary to get up and running with topics.
  • topic tells Rails the name of the new model.
  • title:string says that topics have a title, which is a "string".
  • description:text says that topics have a description which is a "text". A "text" is like a "string" that might be very long.

If you want, take some time to poke around the files listed in this step. You can learn about them in the Rails Architecture page.

Step 2

Type this in the terminal:

Terminal
rails db:migrate

This tells Rails to update the database to include a table for our new model.

Explanation

Databases don't create tables by themselves - they need instructions.

One of the files the scaffold command created will be named something like db/migrate/20170802211140_create_topics.rb. The numbers in the name are the date and time the file was made, so yours will be named differently.

The file contains Ruby code that describes what the table will look like. This is called a migration file. It tells the database how to transform itself into the new configuration.

class CreateTopics < ActiveRecord::Migration[5.1]
  def change
    create_table :topics do |t|
      t.string :title
      t.text :description

      t.timestamps
    end
  end
end

See how this lines up with the scaffold command?

rails generate scaffold topic title:string description:text

The migration says to create a table named "topics", with a title column that's a string, and a description column that's text. Rails automatically adds timestamps, and will use it to automatically record when the data was created and updated.

Rake tasks

rake (ruby make) is a tool that allows you to run small Ruby programs (tasks) that you use often in your application.

Here, rails db:migrate uses a Rake task provided by the Rails framework. It uses the migration file we just created (db/migrate/201xxxxxxxxxxx_create_topics.rb) to change the database. Database migration files can be crucial to code collaboration.

In previous versions of Ruby on Rails, this command would have been run like so: rake db:migrate. Since many developers found it confusing to have some commands run with rails (rails generate, rails server) and some with rake (rake db:migrate, rake -T) they were consolidated. Rake still exists outside of Rails and you may see it from time to time.

You can run rails -T to see a list of all the Rake tasks your app currently responds to, along with a short description of each task.

Next Step:

Go on to CRUD With Scaffolding

Back to Running Your Application Locally