Data Modeling WITH ACTIVE RECORD IN RAILS

About Me:

Hannah HowardTwitter: @techgirlwonderEmail: 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!

• 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

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.

STATIC WebSites VS

Web ApplicationsWeb ApplicationsWeb Applications

Static Web Sites

Server

Give me a page!

Here’s a page!

Client

Static web page: is delivered to the user exactly as stored.

Web APPLICATION

Information

Presented To The User

Data Retrieved From The

Model

Model Of Data

Represented 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 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

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

AcTIVERECORDCheese Typesclass CheeseType < ActiveRecord::Base has_many :cheeses has_and_belongs_to_many :cheese_stores attr_accessible :name, :countryend

Cheesesclass Cheese < ActiveRecord::Base belongs_to :cheese_type belongs_to :cheese_store attr_accessible :weight, :staleend

Cheese Storesclass CheeseStore < ActiveRecord::Base has_many :cheeses has_and_belongs_to_many :cheese_types attr_accessible :name, :addressend

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: Migrations

rails 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 endend

Oh wait, so that’s what rake db:migrate does!

Are You READY TO START PROGRAMMING?

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