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Painted Shadows - Not Allowed Taken from Alexander Calder's mobile room at the National Gallery of Art, Washington DC. MVC Model Associations
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MVC Model Review What key capability do Rails model classes provide?
Browser MVC Model Review What key capability do Rails model classes provide? Ye Olde Internet DB Server View Router Controller Model
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MVC Model Review What key capability do Rails model classes provide?
Browser MVC Model Review What key capability do Rails model classes provide? Ye Olde Internet CRUD persistent data DB Server View Router Controller Model
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MVC Model Review How do you create Rails model classes?
Browser MVC Model Review How do you create Rails model classes? Ye Olde Internet DB Server View Router Controller Model
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MVC Model Review How do you create Rails model classes?
Browser MVC Model Review How do you create Rails model classes? Ye Olde Internet Generate DB migrations and model classes with “rails g model …” then customize DB Server View Router Controller Model
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MVC Model Review What purpose do migrations serve? Ye Olde Internet
Browser MVC Model Review What purpose do migrations serve? Ye Olde Internet DB Server View Router Controller Model
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MVC Model Review What purpose do migrations serve? Ye Olde Internet
Browser MVC Model Review What purpose do migrations serve? Ye Olde Internet Setup tables in DB via “rake db:migrate” and/or “rake db:reset” commands DB Server View Router Controller Model
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MVC Model Review What DB table would go with this model class?
Associated Table: first_name : string last_name : string year : integer Author ???
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MVC Model Review What DB table would go with this model class?
Associated Table: authors first_name : string last_name : string year : integer Author id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940
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Recall Rails ORM (Object-Relational Mapping)
MVC Model Review What DB table would go with this model class? Model Class: Associated Table: authors first_name : string last_name : string year : integer Author Recall Rails ORM (Object-Relational Mapping) id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940
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What Author methods does Rails provide “for free”?
MVC Model Review What Author methods does Rails provide “for free”? Model Class: first_name : string last_name : string year : integer Author
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What Author methods does Rails provide “for free”?
MVC Model Review What Author methods does Rails provide “for free”? Model Class: Many methods: Author.create Author.find Author.find_by Author.all Getters/Setters for attributes Author#first_name Author#first_name= Author#save Author#destroy Author#valid? first_name : string last_name : string year : integer Author
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What customizations might you add to Author?
MVC Model Review What customizations might you add to Author? Model Class: first_name : string last_name : string year : integer Author
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What customizations might you add to Author?
MVC Model Review What customizations might you add to Author? Model Class: Only customization covered so far is data validation first_name : string last_name : string year : integer Author
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Limitation so far: Insular model classes/tables
Associated Table: authors first_name : string last_name : string year : integer Author id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940
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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:
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Requires inter-table references
authors id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 author_profiles id birthplace bio awards 23 Saint Petersburg Rand was born… Prometheus Award, … 42 New York City He was the son of… Shark Conservation, …
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Rails Relationship Support
has one / belongs to one has many / belongs to one has and belongs to many join table Easiest to learn, but narrow in focus Most complex, but also most flexible
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Rails Relationship Support
has one / belongs to one has many / belongs to one has and belongs to many join table
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Has One / Belongs To One Example
first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author profile
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Has One / Belongs To One Example
first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author profile Class Association
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Has One / Belongs To One Example
first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author profile Association Name Triangle indicates reading direction (i.e., Author has AuthorProfile)
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Has One / Belongs To One Example
first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author profile Role Names Like attribute/method name Enables this method call: @author.profile.birthplace
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Has One / Belongs To One Example
first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author profile Multiplicities
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Has One / Belongs To One Example
first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author profile Multiplicities Each Author has 1 AuthorProfile
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Has One / Belongs To One Example
first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author profile Multiplicities Each Author has 1 AuthorProfile Each AuthorProfile is had by 1 Author
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Has One / Belongs To One Example
first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author profile Multiplicities Each Author has 1 AuthorProfile Each AuthorProfile is had by 1 Author More Multiplicities: A B * has Each A has 0 or more Bs 0..* 1..* Each A has 1 or more Bs
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Has One / Belongs To One Example
first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author profile Associated DB Tables authors id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 author_profiles 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, …
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Has One / Belongs To One Example
first_name : string last_name : string year : integer Author birthplace : string bio : text awards : text AuthorProfile has 1 author profile Associated DB Tables authors references id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 author_profiles 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, …
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Primary versus Foreign Keys
Primary Key: Uniquely identifies each record in table authors id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 author_profiles 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, …
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Primary versus Foreign Keys
Primary Key: Uniquely identifies each record in table Foreign Key: Field in table A such that the field is a primary key in one other table B authors id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 author_profiles 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, …
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Primary versus Foreign Keys
Primary Key: Uniquely identifies each record in table Foreign Key: Field in table A such that the field is a primary key in one other table B authors id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 author_profiles 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, …
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Demo Outline Generate AuthorProfile class (no references)
Generate migration to add references Customize model class by adding association Add seed data for AuthorProfile In “show” view, show profile data
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Rails Relationship Support
has one / belongs to one has many / belongs to one has and belongs to many join table
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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 profile title : string year : integer summary : text Book How to model authorship? (assume 1 author per book)
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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 profile has 1 author * book title : string year : integer summary : text Book How to model authorship? (assume 1 author per book)
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Has Many / Belongs to One Example
What should the ORM be? (hint: authors table unchanged) first_name : string last_name : string year : integer Author authors has 1 author * book id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 title : string year : integer summary : text Book
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Has Many / Belongs to One Example
What should the ORM be? (hint: authors table unchanged) first_name : string last_name : string year : integer Author authors has 1 author * book id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 title : string year : integer summary : text Book books id title year summary author_id 72 The Fountainhead 1943 Individualistic architect… 1 98 Atlas Shrugged 1957 Dystopian USA… 99 Jaws 1974 Shark!... 2
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Has Many / Belongs to One Example
What should the ORM be? (hint: authors table unchanged) first_name : string last_name : string year : integer Author authors has 1 author * book id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 title : string year : integer summary : text Book books id title year summary author_id 72 The Fountainhead 1943 Individualistic architect… 1 98 Atlas Shrugged 1957 Dystopian USA… 99 Jaws 1974 Shark!... 2
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Has Many / Belongs to One Example
Rails generates “books” method that returns list of books first_name : string last_name : string year : integer Author authors has 1 author * book id first_name last_name year 1 Ayn Rand 1905 2 Peter Benchley 1940 title : string year : integer summary : text Book books id title year summary author_id 72 The Fountainhead 1943 Individualistic architect… 1 98 Atlas Shrugged 1957 Dystopian USA… 99 Jaws 1974 Shark!... 2
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Demo Outline Generate Books class (no references)
Generate migration to add references Customize model classes by adding association Add seed data for Books In “show” view, show books data
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Rails Relationship Support
has one / belongs to one has many / belongs to one has and belongs to many join table
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Join Table Example From
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Join Table Example Join table
From
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References (aka foreign keys)
Join Table Example References (aka foreign keys) From
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Join Table Example: Model Class
“through” enables this sort of thing: From
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Rails Relationship Support
has one / belongs to one has many / belongs to one has and belongs to many join table For more info, see… Rails Guide Chapter: API Documentation:
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