Rails Decal

Lecture 3 - Models & Migrations

Administrivia

• < 1 hrs
• 1 - 3 hrs
• 3 - 5 hrs
• 5+ hrs

Homework 2 - How long?

Today:

• Database Introduction
• What are Models?
• Creating Models
• Migrations
• Querying the database

How do we persist data?

DATABASES!

What are databases?

• Used to store/retrieve information
• Database is composed of many tables
• Each table corresponds to a Model (explain later)
• Each table has its own set of attributes in columns
• For more in-depth: CS186

Database for sample_app

Databases

Our database of choice

MVC

Models in Rails!

• Models are built in class frameworks
  • Have methods that you don't need to define
  • Interact with the database automatically for you
  • They do a bunch of other cool things like relationships and validations that will be covered later
• They can do all of that because of this:

Why models are important

• Models are the core of Rails apps 
  • Represents all the information you need
    • This allows controllers to work with the model

Future Lectures:

• Validations
• Relationships
• Add more abilities (methods)
• and more!

Creating Models

rails generate model model_name column_name:column_type

Example

rails generate model User name:string age:integer

Migrations

• Migrations change the structure of the database
  • Allows you to add/remove/rename columns
  • Can also create/delete tables

rails generate migration migration_name

Update your database!

rake db:migrate

NEVER CHANGE MIGRATED MIGRATIONS

Types of migrations

Adding columns

Assume we have table called User

add_column :users, :nickname, :string

Removing columns

remove_column :users, :nickname

Renaming columns

rename_column :users, :name, :nickname

Querying our database

Model.find id

Model.find_by attribute: something

Model.where attribute: something

Model.first/last

Model.all

So what can I do with a model? 

• CRUD
  • ​Create
  • Read (Show)
  • Update (Edit)
  • Destroy

CRUD

Today we'll focus on

• Create

CRUD - Create

• Usually done through forms (coming soon!)
• A person on a Rails app will pass in values like
  • Name: Howard
  • Email: swag@swag.com
  • Age: 9001
• And the controller will create a Model Instance
• And add that to the database

Creating our User

Making users locally - Loads our app

rails console OR rails c

Making a new User

user = User.new

user.save!

user = User.create name: "hello", age: 5

`

user.name = "Charles"

OR

Live Demo

• Create user model
• Run migrations to have these work
• Utilize Rails console

Thats cool and all but..

• How do we let the users do it instead of running rails c?
• How to stop erroneous input?

Next time...

• RUD - (Read, Update, Destroy)
• Forms
• Validations

Homework time!

Fork: https://github.com/rails-decal/fa15-hw3

Check in code

dogmodels