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Active Record Data Modeling

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Hannah Howard

This document provides an overview of data modeling with Active Record in Ruby on Rails. It discusses how web applications differ from static websites by retrieving and presenting dynamic data from a model. It then explains that Rails uses a relational database to store data and ActiveRecord to interact with it through objects and queries. It provides examples of modeling data for cheeses, types, and stores with ActiveRecord classes and associations, and examples of common ActiveRecord queries and operations. The document stresses that migrations are key to setting up the database schema that ActiveRecord relies on.

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Data Modeling WITH ACTIVE RECORD IN RAILS
About Me: Hannah Howard Twitter: @techgirlwonder Email: hannah@techgirlwonder.com I run my own computer services business called Tech Girl Wonder.And Im hiring. I do ruby programming with Logical Reality Design, a Rails development shop. Hire us!
This is my take on the subject, not the one true way. For the smarty pants in the room, Im skipping over a lot. Possibly even saying things that arent always true. There will be time for questions. This is not a lecture, only the first 15-30 minutes are. A Few CAVEATS
Why This Talk? I think Ive noticed some patterns in where new people get stuck learning Rails I think it has to do with the parts of Rails that are closer to traditional computer programming and very different from HTML/CSS Specifically, I think people get stuck on the M in the MVC, i.e ActiveRecord and its connection to an SQL database.
STATIC WebSites VS Web Applications Web Applications Web Applications
Static Web Sites Server Give me a page! Heres a page! Client Static web page: is delivered to the user exactly as stored.
Web APPLICATION Informatio n Presented To The User Data Retrieved From The Model Model Of Data Represent ed by App List of changes sent to the model Interface For Receiving Input ServerClient View Controller Gives Input Sees Results
WHAT IS THE MODEL? A model of data represented by the application Rails stores its data in a relational database. (usually) You access data in relational databases with SQL queries SQL queries are complex and hard to write ActiveRecord is there to make that easier and better
What is A RELATIONAL DATABASE? A series of data tables (like Excel spreadsheets) that are connected to each other through relationships Hint: Spend some time with Filemaker or Access
RelationAL Database Example Id Weight Stale 1 6oz TRUE 2 8oz FALSE 3 5oz FALSE Id Name Country 1 Swiss Switzerland 2 American U.S. 3 Harvarty Denmark Id Name Address 1 Cheesetopia 123 Fake St. 2 I Love Cheese 8675 Threeonine Ave. 3 Bobs Cheeses 1 Infinite Loop Cheese Types Cheeses Cheese Shops Id Weight Stale TypeID ShopID 1 6oz TRUE 1 2 2 8oz FALSE 3 3 3 5oz FALSE 2 1 Have Many Have Many Have Many Have Many Belongs To Belongs To TypeID ShopID 3 2 1 2 2 1 1 1 3 3 2 3
SQL: Standard Query Lanaguage SELECT * FROM CHEESES INNER JOIN CHEESE_TYPES ON cheeses.cheese_type_id = cheese_types.id WHERE cheese_types.name IN [SWISS,HARVARTI] WHERE cheeses.stale = FALSE
AcTIVERECORD Cheese Types class CheeseType < ActiveRecord::Base has_many :cheeses has_and_belongs_to_many :cheese_stores attr_accessible :name, :country end Cheeses class Cheese < ActiveRecord::Base belongs_to :cheese_type belongs_to :cheese_store attr_accessible :weight, :stale end Cheese Stores class CheeseStore < ActiveRecord::Base has_many :cheeses has_and_belongs_to_many :cheese_types attr_accessible :name, :address
WoRKING WITH ACTIVE RECORD cheese_type.country = France cheese.cheese_store cheese_store.cheese_types Cheese.where(:weight => 4.0..10.0) Cheese.joins(:cheese_types).where(cheese_types: {name: [SWISS,HAVARTI]}).where(:stale => false)
The KEY PIECE OF GLUE: Migrationsrails generate model cheeses weight:decimal stale:boolean cheese_type_id:integer cheese_store_id:integer class CreateCheeses < ActiveRecord::Migration def change create_table :cheeses do |t| t.decimal :weight t.boolean :stale t.integer :cheese_type_id t.integer :cheese_store_id t.timestamps end end end Oh wait, so thats what rake db:migrate does!
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Active Record Data Modeling

  • 1. Data Modeling WITH ACTIVE RECORD IN RAILS
  • 2. About Me: Hannah Howard Twitter: @techgirlwonder Email: hannah@techgirlwonder.com I run my own computer services business called Tech Girl Wonder.And Im hiring. I do ruby programming with Logical Reality Design, a Rails development shop. Hire us!
  • 3. This is my take on the subject, not the one true way. For the smarty pants in the room, Im skipping over a lot. Possibly even saying things that arent always true. There will be time for questions. This is not a lecture, only the first 15-30 minutes are. A Few CAVEATS
  • 4. Why This Talk? I think Ive noticed some patterns in where new people get stuck learning Rails I think it has to do with the parts of Rails that are closer to traditional computer programming and very different from HTML/CSS Specifically, I think people get stuck on the M in the MVC, i.e ActiveRecord and its connection to an SQL database.
  • 5. STATIC WebSites VS Web Applications Web Applications Web Applications
  • 6. Static Web Sites Server Give me a page! Heres a page! Client Static web page: is delivered to the user exactly as stored.
  • 7. Web APPLICATION Informatio n Presented To The User Data Retrieved From The Model Model Of Data Represent ed by App List of changes sent to the model Interface For Receiving Input ServerClient View Controller Gives Input Sees Results
  • 8. WHAT IS THE MODEL? A model of data represented by the application Rails stores its data in a relational database. (usually) You access data in relational databases with SQL queries SQL queries are complex and hard to write ActiveRecord is there to make that easier and better
  • 9. What is A RELATIONAL DATABASE? A series of data tables (like Excel spreadsheets) that are connected to each other through relationships Hint: Spend some time with Filemaker or Access
  • 10. RelationAL Database Example Id Weight Stale 1 6oz TRUE 2 8oz FALSE 3 5oz FALSE Id Name Country 1 Swiss Switzerland 2 American U.S. 3 Harvarty Denmark Id Name Address 1 Cheesetopia 123 Fake St. 2 I Love Cheese 8675 Threeonine Ave. 3 Bobs Cheeses 1 Infinite Loop Cheese Types Cheeses Cheese Shops Id Weight Stale TypeID ShopID 1 6oz TRUE 1 2 2 8oz FALSE 3 3 3 5oz FALSE 2 1 Have Many Have Many Have Many Have Many Belongs To Belongs To TypeID ShopID 3 2 1 2 2 1 1 1 3 3 2 3
  • 11. SQL: Standard Query Lanaguage SELECT * FROM CHEESES INNER JOIN CHEESE_TYPES ON cheeses.cheese_type_id = cheese_types.id WHERE cheese_types.name IN [SWISS,HARVARTI] WHERE cheeses.stale = FALSE
  • 12. AcTIVERECORD Cheese Types class CheeseType < ActiveRecord::Base has_many :cheeses has_and_belongs_to_many :cheese_stores attr_accessible :name, :country end Cheeses class Cheese < ActiveRecord::Base belongs_to :cheese_type belongs_to :cheese_store attr_accessible :weight, :stale end Cheese Stores class CheeseStore < ActiveRecord::Base has_many :cheeses has_and_belongs_to_many :cheese_types attr_accessible :name, :address
  • 13. WoRKING WITH ACTIVE RECORD cheese_type.country = France cheese.cheese_store cheese_store.cheese_types Cheese.where(:weight => 4.0..10.0) Cheese.joins(:cheese_types).where(cheese_types: {name: [SWISS,HAVARTI]}).where(:stale => false)
  • 14. The KEY PIECE OF GLUE: Migrationsrails generate model cheeses weight:decimal stale:boolean cheese_type_id:integer cheese_store_id:integer class CreateCheeses < ActiveRecord::Migration def change create_table :cheeses do |t| t.decimal :weight t.boolean :stale t.integer :cheese_type_id t.integer :cheese_store_id t.timestamps end end end Oh wait, so thats what rake db:migrate does!
  • 15. Are You READY TO START PROGRAMMING?
  • 17. Lets Start Making It! Tracks Albums Artists Playlists