Rails Decal

Lecture 4 - Models & Migrations

Charles X.

Administrivia

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

Homework 2 - How long?

Administrivia

Starting from HW2, homework due on the following Fridays

Today:

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

How do we persist data?

DATABASES!

What are databases?

 

Text

WAT

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:
class <classname> < ActiveRecord::Base

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/sp15-hw3

Check in code

makingUsers