Design Class Diagrams

1. https://flic.kr/p/9iZYNC Design Class Diagrams

2. Object-Oriented Design “Define software objects and how they collaborate to satisfy their requirements” • Ability to reason about design important! • Understand designer’s intent • Critique/improve the design

3. Source code not best medium for reasoning • Lots of redundancy and irrelevant detail • Poor at depicting relationships among classes in OO programs Solution: Use abstract, visual representations—for example, Design Class Diagrams (DCDs)

4. Overview • Previously: Domain class diagrams • Model problem domain • Today: Design class diagrams • Model Rails model (as in MVC) classes • Also model other software classes (e.g., controller)

5. Design Class Diagrams for Rails Models • Observation: Rails model classes somewhat limited in expressiveness • Thus: Subset of class diagram notation sufficient • Plus a few Rails-model-specific conventions

6. Features of Rails Model • Classes • Attributes • Associations

7. Features of Rails Model • Classes • Attributes • Associations

8. How to model/code a User class and a Sale class?

9. # name :string # email :string class User < ActiveRecord::Base has_many :purchases, :class_name => 'Sale’, :foreign_key => 'buyer_id' has_many :sales, :class_name => 'Sale’, :foreign_key => 'seller_id' end User name : string email : string How to model/code a User class and a Sale class? # price :integer # description :string class Sale < ActiveRecord::Base belongs_to :buyer, :class_name => 'User’, :foreign_key => 'buyer_id' belongs_to :seller, :class_name => 'User’, :foreign_key => 'seller_id’ end Sale price : integer description : string

10. # name :string # email :string class User < ActiveRecord::Base has_many :purchases, :class_name => 'Sale’, :foreign_key => 'buyer_id' has_many :sales, :class_name => 'Sale’, :foreign_key => 'seller_id' end User name : string email : string Commands to generate classes: $ rails generate model User $ rails g model Sale # price :integer # description :string class Sale < ActiveRecord::Base belongs_to :buyer, :class_name => 'User’, :foreign_key => 'buyer_id' belongs_to :seller, :class_name => 'User’, :foreign_key => 'seller_id’ end Sale price : integer description : string

11. # name :string # email :string class User < ActiveRecord::Base has_many :purchases, :class_name => 'Sale’, :foreign_key => 'buyer_id' has_many :sales, :class_name => 'Sale’, :foreign_key => 'seller_id' end User name : string email : string No need to model base class # price :integer # description :string class Sale < ActiveRecord::Base belongs_to :buyer, :class_name => 'User’, :foreign_key => 'buyer_id' belongs_to :seller, :class_name => 'User’, :foreign_key => 'seller_id’ end Sale price : integer description : string

12. Features of Rails Model • Classes • Attributes • Associations

13. Rails Model Attribute Types • :string • :integer • :float • :decimal • :boolean • :primary_key • :text • :binary • :datetime • :timestamp • :time • :date Taken from http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/TableDefinition.html

14. # name :string # email :string class User < ActiveRecord::Base has_many :purchases, :class_name => 'Sale’, :foreign_key => 'buyer_id' has_many :sales, :class_name => 'Sale’, :foreign_key => 'seller_id' end User name : string email : string How to model/code User’s name and email, and Sale’s price and description attributes? # price :integer # description :string class Sale < ActiveRecord::Base belongs_to :buyer, :class_name => 'User’, :foreign_key => 'buyer_id' belongs_to :seller, :class_name => 'User’, :foreign_key => 'seller_id’ end Sale price : integer description : string

15. # name :string # email :string class User < ActiveRecord::Base has_many :purchases, :class_name => 'Sale’, :foreign_key => 'buyer_id' has_many :sales, :class_name => 'Sale’, :foreign_key => 'seller_id' end User name : string email : string How to generate attributes: $ rails g migration add_basic_info_to_users \ name:string email:string $ rails g migration add_basic_info_to_sales \ price:integer description:string # price :integer # description :string class Sale < ActiveRecord::Base belongs_to :buyer, :class_name => 'User’, :foreign_key => 'buyer_id' belongs_to :seller, :class_name => 'User’, :foreign_key => 'seller_id’ end Sale price : integer description : string

16. # name :string # email :string class User < ActiveRecord::Base has_many :purchases, :class_name => 'Sale’, :foreign_key => 'buyer_id' has_many :sales, :class_name => 'Sale’, :foreign_key => 'seller_id' end User name : string email : string Model attributes defined by database migrations (colons part of symbol) # price :integer # description :string class Sale < ActiveRecord::Base belongs_to :buyer, :class_name => 'User’, :foreign_key => 'buyer_id' belongs_to :seller, :class_name => 'User’, :foreign_key => 'seller_id’ end Sale price : integer description : string

17. # name :string # email :string class User < ActiveRecord::Base has_many :purchases, :class_name => 'Sale’, :foreign_key => 'buyer_id' has_many :sales, :class_name => 'Sale’, :foreign_key => 'seller_id' end User name : string email : string Attribute Type Attribute name Colon separator # price :integer # description :string class Sale < ActiveRecord::Base belongs_to :buyer, :class_name => 'User’, :foreign_key => 'buyer_id' belongs_to :seller, :class_name => 'User’, :foreign_key => 'seller_id’ end Sale price : integer description : string

18. Features of Rails Model • Classes • Attributes • Associations

19. Rails Model Class Associations • One-to-one:has_one / belongs_to • One-to-many:has_many / belongs_to • Many-to-many: has_and_belongs_to_many Taken from http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html

20. Class Diagram for has_one Employee Office Has 1 1 employee office

21. Class Diagram for has_one Employee Office Has 1 1 employee office

22. Class Diagram for has_many Manager Employee Has 1 * manager employee

23. Class Diagram for has_many Manager Employee Has 1 * manager employee singular by UMLconvention

24. Class Diagram for has_and_belongs_to_many Programmer Project Has * * programmer project

25. Class Diagram for has_and_belongs_to_many Programmer Project Has * * programmer project Directionunspecified

26. Short/Long Form for Rails Model Associations Short form: class Manager < ActiveRecord::Base has_many:employees, :class_name => Employee, :foreign_key => manager_id end class Employee < ActiveRecord::Base belongs_to:manager, :class_name => Manager, :foreign_key => manager_id end Long form:

27. Short/Long Form for Rails Model Associations Short form: class Manager < ActiveRecord::Base has_many:employees, :class_name => Employee, :foreign_key => manager_id end class Employee < ActiveRecord::Base belongs_to:manager, :class_name => Manager, :foreign_key => manager_id end Long form: Customizable

28. # name :string # email :string class User < ActiveRecord::Base has_many :purchases, :class_name => 'Sale’, :foreign_key => 'buyer_id' has_many :sales, :class_name => 'Sale’, :foreign_key => 'seller_id' end User name : string email : string How to model/code each User “buyer” has many Sale “purchases”? # price :integer # description :string class Sale < ActiveRecord::Base belongs_to :buyer, :class_name => 'User’, :foreign_key => 'buyer_id' belongs_to :seller, :class_name => 'User’, :foreign_key => 'seller_id’ end Sale price : integer description : string

29. # name :string # email :string class User < ActiveRecord::Base has_many :purchases, :class_name => 'Sale’, :foreign_key => 'buyer_id' has_many :sales, :class_name => 'Sale’, :foreign_key => 'seller_id' end User name : string email : string buyer 1 Has # price :integer # description :string class Sale < ActiveRecord::Base belongs_to :buyer, :class_name => 'User’, :foreign_key => 'buyer_id' belongs_to :seller, :class_name => 'User’, :foreign_key => 'seller_id’ end purchase * Sale price : integer description : string

30. # name :string # email :string class User < ActiveRecord::Base has_many :purchases, :class_name => 'Sale’, :foreign_key => 'buyer_id' has_many :sales, :class_name => 'Sale’, :foreign_key => 'seller_id' end User name : string email : string buyer 1 Has # price :integer # description :string class Sale < ActiveRecord::Base belongs_to :buyer, :class_name => 'User’, :foreign_key => 'buyer_id' belongs_to :seller, :class_name => 'User’, :foreign_key => 'seller_id’ end purchase * Sale price : integer description : string

31. # name :string # email :string class User < ActiveRecord::Base has_many :purchases, :class_name => 'Sale’, :foreign_key => 'buyer_id' has_many :sales, :class_name => 'Sale’, :foreign_key => 'seller_id' end User name : string email : string buyer 1 How to model/code each User “seller” has many “sales”? Has # price :integer # description :string class Sale < ActiveRecord::Base belongs_to :buyer, :class_name => 'User’, :foreign_key => 'buyer_id' belongs_to :seller, :class_name => 'User’, :foreign_key => 'seller_id’ end purchase * Sale price : integer description : string

32. # name :string # email :string class User < ActiveRecord::Base has_many :purchases, :class_name => 'Sale’, :foreign_key => 'buyer_id' has_many :sales, :class_name => 'Sale’, :foreign_key => 'seller_id' end User name : string email : string buyer 1 seller 1 Has Has # price :integer # description :string class Sale < ActiveRecord::Base belongs_to :buyer, :class_name => 'User’, :foreign_key => 'buyer_id' belongs_to :seller, :class_name => 'User’, :foreign_key => 'seller_id’ end purchase sale * * Sale price : integer description : string

33. More class diagram notations formodeling design classes

34. UsersController Example UsersController +show() +new() +create() -user_params() : User[*] -@user 1 User

35. Methods UsersController +show() +new() +create() -user_params() : User[*] -@user 1 User

36. Return Type UsersController +show() +new() +create() -user_params() : User[*] 0 or more -@user 1 User

37. Instance Variable UsersController +show() +new() +create() -user_params() : User[*] -@user 1 User

38. Reference to Class Instance UsersController +show() +new() +create() -user_params() : User[*] -@user 1 User

39. Visibility UsersController +show() +new() +create() -user_params() : User[*] + public - private # protected -@user 1 User

40. With these notations, you should be able to express the structure of your object-oriented designsNext time, we’ll cover behavior UsersController +show() +new() +create() -user_params() : User[*] -@user 1 User

41. A word about agile modeling(quoting Larman) Experienced analysts and modelers know thesecret of modeling: Thus, we favor hand-drawn diagrams over typeset ones The purpose of modeling (sketching UML, …) is primarily to understand, not to document. http://flic.kr/p/7SFKjj

42. Tip: Sketch classes starting from the upper left Sale Payment Store address

43. UML class diagrams have even more notations • Two good references: