Chapter 9 - Advanced Active Record

Question 1

ORM

Answer 1

Object-relational mapping framework

Question 2

Scopes

Answer 2

Scopes (or “named scopes” if you’re old school) allow you to define and chain query criteria in a declarative and reusable manner.

scope :submitted, -> { where( submitted: true) }

scope :underutilized, -> { where(‘ total_hours > User.submitted

Question 3

Scope class method

Answer 3

def self.delinquent
  where(' timesheets_updated_at

Question 4

Scope parameters

Answer 4

scope :newer_than, ->( date) { where(‘ start_date > ?’, date) }

BillableWeek.newer_than( Date.today)

Question 5

Chaining scopes

Answer 5

scope :submitted, -> { where( submitted: true) }

scope :underutilized, -> { submitted.where(‘ total_hours

Question 6

default_scope

Answer 6

we can use a default scope to simplify our general queries.

default_scope { where( status: “open”) }

> > Timesheet.pluck(: status)
= > [” open”, “open”, “open”]

Question 7

Arel

Answer 7

Arel is a SQL AST manager for Ruby. It

Simplifies the generation of complex SQL queries
Adapts to various RDBMSes

Question 8

Callbacks

Answer 8

Callbacks can do a variety of tasks, ranging from simple things such as the logging and massaging of attribute values prior to validation to complex calculations.

Question 9

before_save

Answer 9

before_save :geocode

Question 10

pluck

Answer 10

The pluck method queries the database for one or more columns of the underlying table of a model.

User.pluck(: id, :name)

Question 11

Polymorphic has_many Relationships

Answer 11

belongs_to :commentable, polymorphic: true

class Timesheet

Question 12

enum

Answer 12

Rails 4.1

enum status: %i( draft published archived)

> > Post.new.status = > “draft”