Models with ActiveRecord

Agenda

Quiz
Using Ruby to talk to databases
Object-relational Mapping (ORM)
Introduction Active Record
- Required Gems
- Connecting to the Database
- Creating Models
CRUD with Models
- Create
- Read
- Update
- Destroy
Lab/Exercise

QUIZ

What command in psql connects to a database?
What does SQL stand for? What is it meant to do?
What does SERIAL PRIMARY KEY do when assigned to a column?
If I INSERT into a Table, what am I doing?
If I SELECT in a Table, what am I doing?

Using Ruby to talk to databases

Wouldn't it be nice if you could just talk to databases using Ruby?
That'd make life a lot simpler, wouldn't it?
Understanding SQL is important...
But what if we could make our lives as developers just a little bit easier?

Object-relational Mapping (ORM)

ORMs are designed to map databases to Objects
Imagine having an Object that acts as translator between you and SQL!
It is the Babel Fish of SQL!
They really simplify development...
...and make our lives easier

Human Intention behind Active Record

How ORMs Work

ORMs are designed to perform transactions.
When a program makes a request to the database, the transaction begins.
The ORM then translates the request into SQL!
It then attempts to run the SQL query that it created...!
It changes are made to the database and the query was successful the changes are committed.
If the query fails... no changes are made and the transaction is rolled back.
If this occurs, an error is thrown.

Introduction to ActiveRecord

ActiveRecord is an ORM written in Ruby
It was originally designed for Rails
It has been ported to Sinatra and other languages
It is realllllllllllllllyyyyyyyy awesome.

Required Gems

You need to include the following libraries in your Gemfile:

gem 'pg' #postgresql
gem "sinatra-activerecord" #activerecord orm

Connecting to the Database

In your application file, you need to establish a connection to your database using ActiveRecord. We do so by calling the establish_connection method that ActiveRecord provides. We'll pass in the following arguments:

:adapter => "postgresql"
:database => "your_db_name_here"

That's it! From here on out, you can query and modify the database with ease!

Creating Models

To create a model, we need to create a new file.
The structure of the naming should be TablenameModel.rb
We can then include this file using the require('./TablenameModel') command
A model... is simple.
Let's take a look at one!

Sample Model


class Students < ActiveRecord::Base

end

Great, isn't it?

CRUD

CRUD stands for 'create', 'read', 'update' and 'destroy'. You perform these actions on tables inside of your database. Let's imagine that you have the following SQL table named Sms:

id  | message                | sender
-------------------------------------------------
1   | "Hi there!"            | "Kathew"
2   | "sup man."             | "Lichard"
3   | "Just learned Rails!"  | "Kathew"
4   | "hey you guys!"        | "Cecelious"

Create

sms = Sms.new # create a new
sms.message = "Hi there!" # add values
sms.sender = "Kathew"
sms.save      # saves to the database

Read

Find an object in a list of objects

sms = Sms.find(2) # find by id
# => sms = { id: 2, message: "sup man.", sender: "Lichard" }
sms.message
# => "sup man."
sms[:message]
# => "sup man."

Update

sms = Sms.find(4) # find by id
sms.sender = "sms ninja" # update a value
sms.save # save to database

Destroy

sms = Sms.find(1) # find by id
sms.destroy # delete from database

Conclusion

Is ActiveRecord awesome?
Yes?
Ready to use it?

Lab

Migrations to Models

We're going to create a students app based on our dragons database!
We need to connect to our database!
We need to create Models for our Students table!
We need to add items using ActiveRecord!
We need to read them via JSON!

Models with ActiveRecord