Сергей Нартымов (Software Engineer в Transinet GmbH, г.Минск) Доклад: «Работа с базами данных с использованием Sequel» О чём: Ruby библиотека для работы с базами данных Sequel представляет собой легковесную альтернативу более популярной Active Record. Sequel лежит в основе работы с SQL базами данных в ROM (Ruby Object Mapper) - развивающемся ORM для Ruby, реализующим паттерн Data Mapper. В докладе будут рассмотрены различные аспекты использования Sequel, в том числе показаны примеры использования некоторых возможностей PostgreSQL с помощью Sequel.

1. Работа&с&базами&данных
с"использованием"Sequel

3. Dependencies

5. Sequel&has&restored&my&faith&in&
Ruby.&It's&really&amazing.&The&O/RM&
I've&been&hoping&for&for&years.
—"Sam"Smoot,"creator"of"DataMapper

6. Database
# memory database
DB = Sequel.sqlite
# connection string
DB = Sequel.connect('postgres://host/database')

7. Database
DB.create_table(:users) do
primary_key :id
String :name
end

8. Migra&ons
Sequel.migration do
change do
create_table(:users) do
primary_key :id
String :name
end
end
end

9. Dataset
dataset = DB[:users] # SELECT * FROM "table"
dataset = DB.from(:users) # SELECT * FROM "table"
dataset = DB.select(:column) # SELECT "column"

10. Dataset
dataset = DB[:test].
select(:first_name, :last_name).
where(country: 'BY').
order(:created_at)

11. Dataset
dataset.first
dataset.all
dataset.each { |row| row }

12. Dataset
dataset.insert(last_name: 'Test')
dataset.update(last_name: 'Test')
dataset.delete

13. Virtual(Row(Blocks
dataset.where(Sequel.expr(:a) > Sequel.function(:b, :c))
# WHERE a > b(c)
dataset.where { a > b(c) }

14. Model
class User < Sequel::Model
one_to_many :posts
end

15. Model
• many_to_one
• one_to_many
• one_to_one
• many_to_many
• one_through_one

16. Model
class User < Sequel::Model
def validate
super
validates_presence :name
end
end

17. Model
class User < Sequel::Model
def before_create
# do something
super
end
def after_update
super
# do something
end
end

18. Model
user = User[1234]
user.name = 'Test'
user.save

19. Types
• pg_array
• pg_hstore
• pg_inet
• pg_interval
• pg_json
• pg_range

20. pg_array_associa+ons
# Database schema:
# tags albums
# :id (int4) <-- :id
# :name -- :tag_ids (int4[])
# :name
class Album
plugin :pg_array_associations
pg_array_to_many :tags
end
class Tag
plugin :pg_array_associations
many_to_pg_array :albums
end

21. Constraints
create_table(:users) do
primary_key :id
String :name
constraint(:name_min_length) { char_length(name) > 2 }
end

22. Indexes
alter_table(:users) do
add_index Sequel.function(:lower, :name), name: :lower_name
end
# CREATE INDEX "lower_name" ON "users" (lower("name"))

23. Func%ons/Triggers
DB.create_function(:set_updated_at, <<-SQL, language: :plpgsql, returns: :trigger)
BEGIN
NEW.updated_at := CURRENT_TIMESTAMP;
RETURN NEW;
END;
SQL
# CREATE FUNCTION set_updated_at() RETURNS trigger LANGUAGE plpgsql AS '
# BEGIN
# NEW.updated_at := CURRENT_TIMESTAMP;
# RETURN NEW;
# END;'
DB.drop_function(:set_updated_at)
# DROP FUNCTION set_updated_at()

24. Func%ons/Triggers
DB.create_trigger(:table, :trg_updated_at, :set_updated_at,
events: :update, each_row: true,
when: { new__updated_at: :old__updated_at })
# CREATE TRIGGER trg_updated_at BEFORE UPDATE ON "table"
# FOR EACH ROW WHEN ("new"."updated_at" = "old"."updated_at")
# EXECUTE PROCEDURE set_updated_at()
DB.drop_trigger(:table, :trg_updated_at)
# DROP TRIGGER trg_updated_at ON "table"

25. sequel_postgresql_triggers
• pgt_created_at
• pgt_updated_at
• pgt_counter_cache
• pgt_sum_cache
• pgt_immutable
• pgt_touch

26. Window'Func+ons
SELECT
lag(timestamp) OVER (ORDER BY timestamp),
timestamp
FROM events

27. Window'Func+ons
DB[:events]
.select { [lag(timestamp).over(order: :timestamp),
timestamp] }

28. Common%Table%Expressions
WITH moved_rows AS (
DELETE FROM products
WHERE "date" BETWEEN '2010-10-01' AND '2010-10-31'
RETURNING *
)
INSERT INTO products_log
SELECT * FROM moved_rows;
DB[:products_log].
with(:moved_rows,
DB[:products].
where(date: Date.new(2010, 10, 1)..Date.new(2010, 10, 31)).
returning.
with_sql(:delete_sql)).
insert(DB[:moved_rows])

29. Recursive)Common)Table)
Expressions

30. rcte_tree
• h#p://sequel.jeremyevans.net/rdoc8plugins/classes/Sequel/
Plugins/RcteTree.html
• h#p://explainextended.com/2009/09/24/adjacency8list8vs8
nested8sets8postgresql/

31. Prepared'transac,ons
DB.transaction(prepare: 'some_transaction_id_string') do
# ...
end
DB.commit_prepared_transaction('some_transaction_id_string')
DB.rollback_prepared_transaction('some_transaction_id_string')

32. Cursors
DB[:table].use_cursor.each { |row| }
# BEGIN;
# DECLARE sequel_cursor NO SCROLL CURSOR WITHOUT HOLD FOR SELECT * FROM "table";
# FETCH FORWARD 1000 FROM sequel_cursor
# FETCH FORWARD 1000 FROM sequel_cursor
# ...
# FETCH FORWARD 1000 FROM sequel_cursor
# CLOSE sequel_cursor
# COMMIT
DB[:table].paged_each { |row| }

33. Streaming
gem 'sequel_pg'
DB.extension(:pg_streaming)
DB[:table].stream.each { |row| }
DB[:table].paged_each { |row| }

34. Plugins
h"p://sequel.jeremyevans.net/plugins.html

35. Documenta*on
h"p://sequel.jeremyevans.net/documenta7on.html