sheesh19 / active-record-vali-488

ActiveRecord Boilerplate

This is a starting point for the Activerecord Basics lecture using sqlite. During the lecture, you need to:

• Clone The project
• Run bundle install
• Explain rake -T
• Explain config/database.yml
• Run rake db:create / rake db:drop
• Create and run 2 migrations

REVIEW

• Relational Database: tables representing data and tables can be related to one another through foreign keys (ids)

• Relationships: 1:N, N:N, 1:1

• SQL CRUD (characters as our table)

• SQL is the language for relational databases

READ ALL for SQL

• SELECT * FROM characters;

READ ONE for SQL

• SELECT * FROM characters WHERE id = 1;

CREATE

• INSERT INTO

UPDATE

• UPDATE SET

DELETE

• DELETE FROM

FILTERS

• ORDER BY << sorts results in order (ASC / DESC)
• COUNT << returns # of items that meet the criteria
• GROUP BY << groups results by specified column / criteria

JOIN

JOIN table_name ON column_one.id = column_two.column_one_id

ACTIVE RECORD

• Active Record: design pattern, allows you to interact with DB through Ruby methods which are inherited, ActiveRecord is a gem. Links one record in our database to one instance of our Class.

RAKE TASKS

• CREATE: rake db:create

• DROP: rake db:drop

• MIGRATE: rake db:migrate

• Migrations: change the structure of the database / schema (add a table, new column, drop a table)

ACTIVE RECORD CRUD (characters)

READ ALL

• Character.all

READ ONE

• Character.find(1)
• Character.find_by(name: 'Harry Potter') # returns first one

FILTERED MANY

• Character.where(address: 'Hogwarts') # returns all as an ARRAY

CREATE

• Character.create(name: 'Harry Potter')
• character = Character.new(name: 'Harry Potter')
• character.save

UPDATE

• character = Character.find(1)
• character.name = 'Voldemort'
• character.save

DELETE

• character = Character.find(1)
• character.destroy

ADVANCED

• Character.last
• Character.first
• Character.first(5)
• Character.count