What in the world is ActiveRecord?

A: (sweet ruby) MAGIC in the form of a Design Pattern!

Let’s start with SQL!Wait what? That’s not ActiveRecord

• SQL stands for Structured Query Language• There are a ton of different SQL Databases!!

• SQL lets you manage data in a relational database• Insert - Create a new row of information in a table• Update - Change information in an existing row• Select - Retrieve information in a table• Delete - Remove a row in a table

• SQL uses data types such as String, Text, Integer, Date, Time

• An SQL query looks like this: SELECT * FROM cats WHERE cats.breed = ‘Sphynx’;

How does SQL even…?

Doing it the Ruby Way

Active Record PatternConvention over Configuration

(CoC)Don’t Repeat Yourself (DRY)Model-View-Controller (MVC)

• Some Frameworks require you to write a lot of configuration code.

• Rails Adopts Conventions so you don’t have to!1. Naming Conventions2. Schema Conventions3. Query Interface

Ruby on Rails Guides: http://guides.rubyonrails.org/active_record_basics.html#convention-over-configuration-in-active-record

What’s an ORM?• ORM stands for Object Relational Mapper• Maps database to ruby object• They get rid of SQL queries in code SELECT * FROM cats VS Cats.all

• Essentially ActiveRecord takes ruby code and translates it into SQL code.

Hint: Active Record is Ruby’s way of dealing with ugly SQL!

Active Record is the “M” in MVC

model: DOGGIEid name color spotted adorable age

1 Chowderhead tan and white FALSE TRUE 1

2 Paco snow white FALSE TRUE 3

3 Tenley brown and white spots

TRUE TRUE 5

Models are Ruby classes. • They talk to the database• Store and validate data• Performs the logic of

knowing about an instance of itself

So… what is a MODEL anyway??

Active Record RelationshipsHow Do Models Connect with Each Other?

Lets start easy:A Supplier has one Account

(This is a One-to-One Relationship)

Alternately,an Order belongs to a Customer

(Also, a One-to-One Relationship)

More Active Record Relationships

And when a Doctor has many Patients,but a Patient has many Doctors too!

…and they both have many Appointments!

So Why Associations?

• Make ugly SQL statements Ruby-Friendly:

SELECT surveys FROM surveys JOIN ON users WHERE user.name LIKE “Dicko”

—becomes—

dicko = User.find_by_name(“Dicko”)dicko.surveys

• We are basically making wonderful Ruby Methods with each association we declare!

• Remember: IT ONLY LOOKS LIKE MAGIC (it never is)