3. 80
60
40
20
0
2007 2008 2009

11. Po w ere d by vs

17. class Employee < ActiveRecord::Base
validates_presence_of :name
CREATE TABLE employees (
name VARCHAR(40) NOT NULL,

18. class Employee < ActiveRecord::Base
validates_length_of :login,
:minimum => 5
CREATE TABLE employees (
login VARCHAR(10)
check(length(login) > 4),

19. begin
emp = Employee.new(:login => '')
emp.save_with_validation(false)
fail
rescue ActveRecord::StatementInvalid
end

20. Departments Employees

21. class Employee < ActiveRecord::Base
belongs_to :department
validates_presence_of :department
CREATE TABLE employees (
department_id INTEGER NOT NULL
REFERENCES departments(id),

24. Companies Departments Employees

25. has_many :though
company.employees.size
SELECT count(*) AS count_all
FROM employees
INNER JOIN departments
ON employees.department_id =
departments.id
WHERE departments.company_id = 1

26. SELECT count(*) AS count_all
FROM employees
WHERE company_id = 1
Companies
?
Departments Employees

27. company_id department_id
Companies Departments Employees
id id id
company_id company_id
department_id

28. Companies Departments Employees
id company_id id
department_id company_id
department_id

29. departments
CREATE TABLE departments(
company_id INTEGER NOT NULL
REFERENCES companies(id),
department_id SERIAL NOT NULL,
PRIMARY KEY (company_id,
department_id)

30. employees
CREATE TABLE employees(
company_id INTEGER NOT NULL
REFERENCES companies(id),
department_id INTEGER NOT NULL,
FOREIGN KEY
(company_id, department_id)
REFERENCES department
(company_id, department_id)

31. departments company_id
department_id employees
Companies Departments Employees
id company_id id
department_id company_id
department_id

32. # gem install composite_primary_keys

33. Department
class Department < ActiveRecord::Base
set_primary_keys :company_id,
:department_id
has_many :employees,
:foreign_keys =>
[:company_id,
:department_id]

34. Company
class Company < ActiveRecord::Base
def employees_size
Employee.count(
:conditions =>
['company_id = ?', id])
end

38. CREATE VIEW big_campanies AS
SELECT * FROM companies WHERE id IN
(SELECT company_id FROM
(SELECT compay_id, count(id) AS c
FROM employees
GROUP BY company_id) AS t
WEHRE c > 1000)

39. BigCampany
class BigCampany < ActiveRecord::Base
has_many :department
end

40. SELECT * FROM (SELCT * FROM ...)