This document discusses single table inheritance (STI) in Rails. STI allows subclasses to share a single database table with a parent class. It avoids data redundancy and takes an object-oriented approach. STI is best when objects have many identical attributes but different behaviors. Benefits include simplicity and faster queries, while drawbacks include tight coupling and inability to change an object's type after creation. The document provides examples of implementing STI and considers when it is and isn't appropriate.

1. Single Table
Inheritance
http://jyaasa.comCopyright 2016. Jyaasa Technologies.

2. Hi all,
I am Surya Prasad Siwakoti
Associate Software Engineer
Jyaasa Technologies
http://jyaasa.comCopyright 2016. Jyaasa Technologies.

3. Objectives
● Introduction to STI (Single Table Inheritance)
● When to use STI
● How to implement STI
● When not to use STI
● Demo

4. Why Single Table Inheritance
● Avoid Data Redundancy (DRY principle)
● Object Oriented way instead of Database
Relational approach between two objects
● Single table for multiple model

5. create_table :stylist do
|t|
t.id :integer
t.date :date_of_birth
t.string :first_name
t.string :last_name
t.string :email
t.sign_in_count
:integer
t.string :password
t.string :gender
end
Data Redundancy
create_table :customer do |t|
t.id :integer
t.date :date_of_birth
t.string :first_name
t.string :last_name
t.string :email
t.sign_in_count :integer
t.string :password
t.string :gender
end

6. class User < ActiveRecord::Base
end
class Stylist < User
end
class Customer < User
end
Object Oriented way instead of Database
Relational approach between two objects

7. What is Single Table Inheritance?
● STI allows you to create subclasses of a particular database
table.
● Eg: Parent class: user, Child class: stylist, customer
● Using a single table for multiple objects

8. When to Use STI
When there are two or more than two objects which have
same attributes but different behaviours.

9. class User < ActiveRecord::Base
end
class Stylist < User
def requested_or_verified?
profile.requested? || profile.verified?
end
end
class customer < User
def habbit_image
return ‘default-photo’ if
habit_image.blank?
end
end
Stylist.new({
first_name: “surya”
})
Stylist.last.first_name
=> “surya”
Customer.new({
first_name: “sarbada”
})
Customer.last.first_name
=> “sarbada”

10. Benefits of STI
1. Simple approach
● Create a model class eg: stylist
● Inherit from a user
● Create a type field with string data type in user table
2. No more gems
3. OO way
4. Faster query
A single query in one table is enough for retrieving data.
3. DRY Principle
● DRY controller
● No redundant data in table

11. Drawbacks Of STI
● Tightly coupled parent model
● Changes to the database affects controller and view codes.
● Child class database field should not have too many unique attributes.
● We cannot change object class in runtime. An object life cycle should
finish.
a = Stylist.first
a.type = “Customer”
a.class.name
a.reload!
● Forces to save nullable/empty columns.

12. a.update_attributes(type:
"ShippingAddress", country: "Spain") #
=> true # but should be false
a.class.name # => "BillingAddress" #
But we wanted ShippingAddress
a.valid? # => true # but should be
false, we ship only to USA and Canada
class Address < ActiveRecord::Base
validates_presence_of :full_name,
:city, :street, :postal_code
end
class BillingAddress < Address
validates_presence_of :country
end
class ShippingAddress < Address
validates_inclusion_of :country,
in: %w(USA Canada)
end
Type Change Drawback

13. ● Arkency Blog. 2016. Single Table Inheritance - Problems and solutions - Arkency
Blog. [ONLINE] Available at: http://blog.arkency.com/2013/07/sti/. [Accessed 20
June 2016].
● FutureLearn. 2016. Refactoring our Rails app out of single-table inheritance.
[ONLINE] Available at: https://about.futurelearn.com/blog/refactoring-rails-sti/.
[Accessed 20 June 2016].
● Eugene Wang. 2016. How (and When) to Use Single Table Inheritance in Rails -
eugenius. [ONLINE] Available at: http://eewang.github.io/blog/2013/03/12/how-and-
when-to-use-single-table-inheritance-in-rails/. [Accessed 20 June 2016].
References

15. Thank you