Sequel is a Ruby ORM and database toolkit that provides an ActiveRecord-like interface for working with databases. It supports SQLite, MySQL, PostgreSQL, and other databases. With Sequel, you can connect to databases, run SQL queries to retrieve and manipulate data, define models, and establish associations between models. Queries can be chained and return dataset objects. Sequel offers features like validations, hooks, migrations, and transactions for managing models and data.

1. Sequel
pure Ruby DB Toolkit

2. http://sequel.rubyforge.org/

3. Ruby Toolbox
• Database Abstraction - Adapters
• DSL - Ruby
• ORM - Models

4. Adapters
• SQLite
• MySQL (2)
• PostgreSQL
• DBI

5. gem install sequel
gem install sqlite3
gem install mysql2

6. Connect to DB
• DB = Sequel.sqlite (in-memory)

7. Connect to DB
• DB = Sequel.sqlite (in-memory)
• DB = Sequel.connect (‘sqlite://test.db’)

8. Connect to DB
• DB = Sequel.sqlite (in-memory)
• DB = Sequel.connect (‘sqlite://test.db’)
• DB = Sequel.connect (‘mysql://...’)
• DB = Sequel.connect (‘postgres://...’)

9. Ruby Toolbox
sequel -E sqlite://test.db

10. Database Object

11. DB - Database Object
• DB.tables
• DB.table_exists?(:items)
• DB.schema(:items)
• DB.add_index :items, :name

12. SQL QUIZ !
Rename table

13. SQL QUIZ !
DB.rename_table
:items , :mono

14. SQL QUIZ !
ALTER TABLE `items`
RENAME TO `mono`

16. DB.run(‘ALTER TABLE ’)
DB.rename_table

17. Dataset Object

18. Unique for Sequel

19. Dataset object
SQL Query
as
Object

20. DB[:items]

21. Immutable
Dataset
Return
Dataset (copy)

22. Chainable
DB[:Items]
SELECT * FROM `items`

23. Chainable
DB[:Items] where(‘price > 10’)
SELECT * FROM `items`
WHERE (price > 100)

24. Chainable
DB[:Items] where(‘price > 10’) order(:name) limit(10)
SELECT * FROM `items`
WHERE (price > 100)
ORDER BY `name` LIMIT 10

25. Two type of returns
Dataset return Dataset’
id name
Dataset return
1 a
2 b
DB[:items].limit(10).all

26. require ‘sequel_core’

27. Model

28. require ‘sequel’
class Item < Sequel::Model
Dataset
end

29. Associations
class Item < Sequel::Model
many_to_one :users
end
class User < Sequel::Model
one_to_many :items
end

30. Associations
ActiveRecord Sequel
belongs_to many_to_one
has_many one_to_many
has_and_belongs_to... many_to_many
has_one one_to_one

31. Other features
• Model validations - validate_*
• Model hooks - before, after
• Migrations
• Transactions

32. Questions?