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associations.pptx
- 4. Ye Olde Internet Server Router Controller View Browser Model DB MVC Model Review What key capabilities do Rails model classes provide?
- 5. Ye Olde Internet Server Router Controller View Browser Model DB MVC Model Review What key capability do Rails model classes provide? CRUD persistent data
- 6. Ye Olde Internet Server Router Controller View Browser Model DB MVC Model Review How do you create Rails model classes?
- 7. Ye Olde Internet Server Router Controller View Browser Model DB MVC Model Review How do you create Rails model classes? Generate DB migrations and model classes with “rails g model …” then customize
- 8. Ye Olde Internet Server Router Controller View Browser Model DB MVC Model Review What purpose do migrations serve?
- 9. Ye Olde Internet Server Router Controller View Browser Model DB MVC Model Review What purpose do migrations serve? Setup tables in DB via, e.g., “rails db:migrate” command
- 10. MVC Model Review What DB table would go with this model class? first_name : string last_name : string year : integer Author Model Class: Database Table: ???
- 11. MVC Model Review What DB table would go with this model class? id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 authors first_name : string last_name : string year : integer Author Model Class: Database Table:
- 12. MVC Model Review What DB table would go with this model class? id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 authors first_name : string last_name : string year : integer Author Model Class: Database Table: Recall Rails ORM (Object-Relational Mapping)
- 13. MVC Model Review What Author methods does Rails provide “for free”? first_name : string last_name : string year : integer Author Model Class:
- 14. MVC Model Review What Author methods does Rails provide “for free”? first_name : string last_name : string year : integer Author Model Class: Many methods: • Author.create / Author.create! • Author.find • Author.find_by • Author.all • Getters/Setters for attributes: ⎼ Author#first_name ⎼ Author#first_name= • Author#save / Author#save! • Author#destroy • Author#valid?
- 15. id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 authors first_name : string last_name : string year : integer Author Model Class: Limitation so far: Insular model classes/tables Database Table:
- 16. id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 authors first_name : string last_name : string year : integer Author Model Class: Imagine an author-profile class Database Table: birthplace : string bio : text awards : text AuthorProfile id birthplace bio awards 23 Saint Petersburg Rand was born… Prometheus Award, … 42 New York City He was the son of… Shark Conservation, … author_profiles
- 17. What if you want inter-class relationships? first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile ??? For example, you might want to say:
- 18. Rails Model Associations Topics: • OO Class Associations • Rails ORM • How to code in Rails
- 19. Rails Model Supports Three Associations A B 1 has ▶︎ one to one (has one / belongs to one) A B * has ▶︎ one to many (has many / belongs to one) A B * many to many (join table) 1 1 * AB
- 20. first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author 1 profile Class Association Notation
- 21. first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author 1 profile Class Association Notation Class Association
- 22. first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author 1 profile Class Association Notation Association Name Triangle indicates reading direction (i.e., Author has AuthorProfile)
- 23. first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author 1 profile Class Association Notation Role Names Like attribute/method name Enables this method call: @author.profile.birthplace
- 24. first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author 1 profile Class Association Notation Multiplicities
- 25. first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author 1 profile Class Association Notation Multiplicities Each Author has 1 AuthorProfile
- 26. first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author 1 profile Class Association Notation Multiplicities Each Author has 1 AuthorProfile Each AuthorProfile belongs to 1 Author
- 27. first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author 1 profile Class Association Notation Multiplicities Each Author has 1 AuthorProfile Each AuthorProfile belongs to 1 Author Zero-or-More Multiplicities: A B * has Each A has 0 or more Bs A B 0..* has Each A has 0 or more Bs
- 28. first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author 1 profile Class Association Notation first_name = "Ayn" last_name = "Rand" year_born = 1905 : Author first_name = "Peter" last_name = "Benchley" year_born = 1940 : Author birthplace = "Saint Petersburg" bio = "Rand was born..." awards = "Prometheus Award, …" : AuthorProfile birthplace = "New York City" bio = "He was the son of..." awards = " Shark Conservation, … " : AuthorProfile Associations manifest as links in object diagrams author profile author profile
- 29. Class Association Notation name : string Physician name : string Patient * physician * patient appointment_date : datetime Appointment Association Class Each instance is an association link Can add additional data to each link (e.g., date)
- 30. name : string Physician name : string Patient * physician * patient appointment_date : datetime Appointment Enables code like this: Class Association Notation
- 31. name : string Physician name : string Patient * physician * patient appointment_date : datetime Appointment Class Association Notation name = "Dr. Hibbert" : Physician name = "Homer Simpson" : Patient name = "Marge Simpson" : Patient appointment_date = ... : Appointment appointment_date = ... : Appointment physician patient physician patient How many-to-many links look in object diagrams:
- 32. Rails Model Associations Topics: • OO Class Associations • Rails ORM • How to code in Rails
- 33. first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author 1 profile To map this association to relational DB... first_name = "Ayn" last_name = "Rand" year_born = 1905 : Author first_name = "Peter" last_name = "Benchley" year_born = 1940 : Author birthplace = "Saint Petersburg" bio = "Rand was born..." awards = "Prometheus Award, …" : AuthorProfile birthplace = "New York City" bio = "He was the son of..." awards = " Shark Conservation, … " : AuthorProfile author profile author profile
- 34. id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 authors id birthplace bio awards 23 Saint Petersburg Rand was born… Prometheus Award, … 42 New York City He was the son of… Shark Conservation, … author_profiles Requires inter-table references
- 35. Rails ORM Varies by Type of Association A B 1 has ▶︎ one to one (has one / belongs to one) A B * has ▶︎ one to many (has many / belongs to one) A B * many to many (join table) 1 1 * AB
- 36. first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author 1 profile Has One / Belongs To One Example id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 authors id author _id birthplace bio awards 23 1 Saint Petersburg Rand was born… Prometheus Award, … 42 2 New York City He was the son of… Shark Conservation, … author_profiles Rails ORM DB Tables
- 37. first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author 1 profile Has One / Belongs To One Example id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 authors id author _id birthplace bio awards 23 1 Saint Petersburg Rand was born… Prometheus Award, … 42 2 New York City He was the son of… Shark Conservation, … author_profiles Rails ORM DB Tables
- 38. id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 authors id author _id birthplace bio awards 23 1 Saint Petersburg Rand was born… Prometheus Award, … 42 2 New York City He was the son of… Shark Conservation, … author_profiles Primary versus Foreign Keys Primary Key: Uniquely identifies each record in table
- 39. id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 authors id author _id birthplace bio awards 23 1 Saint Petersburg Rand was born… Prometheus Award, … 42 2 New York City He was the son of… Shark Conservation, … author_profiles Primary versus Foreign Keys Primary Key: Uniquely identifies each record in table Foreign Key: Reference to primary key in another table
- 40. id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 authors id author _id birthplace bio awards 23 1 Saint Petersburg Rand was born… Prometheus Award, … 42 2 New York City He was the son of… Shark Conservation, … author_profiles Primary versus Foreign Keys Primary Key: Uniquely identifies each record in table Foreign Key: Reference to primary key in another table
- 41. How to Set Up Association in Rails 1. Generate migration that adds reference (foreign key) column to appropriate table 2. Add has_one/belongs_to declarations to model class See forthcoming demo for details
- 42. Rails Relationship Support • has one / belongs to one • has many / belongs to one • join table
- 43. Has Many / Belongs to One Example first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author 1 profile title : string year : integer summary : text Book How to model authorship? (assume 1 author per book)
- 44. Has Many / Belongs to One Example first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author 1 profile title : string year : integer summary : text Book How to model authorship? (assume 1 author per book) has 1 author * book
- 45. Has Many / Belongs to One Example first_name : string last_name : string year : integer Author title : string year : integer summary : text Book What should the ORM be? (hint: authors table unchanged) has 1 author * book id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 authors
- 46. Has Many / Belongs to One Example first_name : string last_name : string year : integer Author title : string year : integer summary : text Book What should the ORM be? (hint: authors table unchanged) has 1 author * book id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 authors id title year summary author_id 72 The Fountainhead 1943 Individualistic architect… 1 98 Atlas Shrugged 1957 Dystopian USA… 1 99 Jaws 1974 Shark!... 2 books
- 47. Has Many / Belongs to One Example first_name : string last_name : string year : integer Author title : string year : integer summary : text Book What should the ORM be? (hint: authors table unchanged) has 1 author * book id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 authors id title year summary author_id 72 The Fountainhead 1943 Individualistic architect… 1 98 Atlas Shrugged 1957 Dystopian USA… 1 99 Jaws 1974 Shark!... 2 books
- 48. Has Many / Belongs to One Example first_name : string last_name : string year : integer Author title : string year : integer summary : text Book has 1 author * book id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 authors id title year summary author_id 72 The Fountainhead 1943 Individualistic architect… 1 98 Atlas Shrugged 1957 Dystopian USA… 1 99 Jaws 1974 Shark!... 2 books Rails generates books method that returns list of books
- 49. How to Set Up in Rails • Essentially the same as has_one • Again, see the demo
- 50. Rails Relationship Support • has one / belongs to one • has many / belongs to one • join table
- 51. Example Many-to-Many Association name : string Physician name : string Patient * physician * patient appointment_date : datetime Appointment
- 52. Join Table Example From http://guides.rubyonrails.org/v4.2.0/association_basics.html
- 53. Join Table Example Join table From http://guides.rubyonrails.org/v4.2.0/association_basics.html
- 54. Join Table Example References (aka foreign keys) From http://guides.rubyonrails.org/v4.2.0/association_basics.html
- 55. Join Table Example: Model Class through enables this sort of thing: From http://guides.rubyonrails.org/v4.2.0/association_basics.html
- 56. How to Set Up in Rails • See the Model Association demos • For more info: – http://guides.rubyonrails.org/v6.1.0/association_basics.html – http://api.rubyonrails.org/v6.1.0/classes/ActiveRecord/Asso ciations/ClassMethods.html
- 57. Summary • Model associations • Foreign keys • Rails ORM for assoc. • Has-one/belong-to-one • Has-many/belongs-to-one • Many-to-many join table http://flic.kr/p/aCLor3
Notes de l'éditeur
- Painted Shadows - Not Allowed Taken from Alexander Calder's mobile room at the National Gallery of Art, Washington DC.