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.

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 I’m 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, I’m skipping over a lot.
Possibly even saying things that aren’t 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 I’ve 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!
Here’s 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 Bob’s 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 that’s what rake db:migrate does!

15. Are You READY TO START
PROGRAMMING?

16. rb-tunes
Our Project:
iTunes

17. Lets Start Making It!
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