2023-05-08 - Active Record

• back to Le Wagon's Bootcamp log.
• link to the lecture

main topics

• Active Record
• some details about rake
  • rake -T is your friend :)
• Migrations

Active Record

From RoR docs:

Active Record is the M in MVC - the model - which is the layer of the system responsible for representing business data and logic. Active Record facilitates the creation and use of business objects whose data requires persistent storage to a database. It is an implementation of the Active Record pattern which itself is a description of an Object Relational Mapping system.

Link to the "Active Record Pattern" article by Martin Fowler.

rake

# show all tasks
rake -T

# load the app config inside an irb session
rake console

Migrations

Each time you change your schema (add/remove table/column) you need to create a schema migration.

It's a change in the structure of your schema, not the data.

Example

timestamp="$(date +'%Y%m%d%H%M%S')"

# as restaurants is in plural, it's implicit
# that it's a table.
db/migrate/${timestamp}_create_restaurants.rb

contents of the *_create_restaurants.rb:

class CreateRestaurants < ActiveRecord::Migration[7.0]
  def change
    create_table :restaurants do |t|
      t.string :name
      t.string :address
      t.timestamps # for created_at and updated_at
    end
  end
end

Notes about conventions for migrations:

• the filename is in lower_snake_case
• the class name is in CapitalizedCamelCase
• in the example above we're creating a table, therefore it's going to be in plural (when a migration refers to a column, it's not written in plural).

PAREI em 28min!!

Naming conventions

• table
• model
• class

pluralization is handled beautifully by Active Record.

Sequence

• draw table in db.lewagon.com
• write the migration files
• run rake db:migrate
• write the models

Validation

uniqueness

• Use unique: true in the migration column configuration
• Use uniqueness: true in the model validates configuration