day_2

Validations and Associations

Routes as Resources

• If you have a "resource," as defined by the need to perform all (or most) CRUD operations, you can use the resources method in your routes:

resources :users

• This will create routes for each CRUD operation according to the convention.
• You can view your available routes by running rake routes.

Introduction to Data Validation

• Validations allow us to make sure that the data we are trying to save to the database is in a correct format.
• Think of email addresses: you may want to make sure the email is properly formatted and not just a simple piece of text.
• Also, think of passwords: you may want to make sure they are a certain number of characters and contain at least one letter and one uppercase letter.
• There are many validations we can perform. A good list can be found here.
• All validations occur on the model side.

Using Validations

• Validations are placed in the model in a "shortcut" type format or a more verbose format.
• If any of these validations fail, the "transaction" is rolled back and the data is not saved to the database.

Shortcut:

validates :COL_NAME, 
    presence: true, 
    length: { :maximum => 50 }, 
    numericality: false, 
    uniqueness: true

Verbose:

validates_presence_of :first_name
validates_presence_of :last_name

or

validates :first_name, presence: true
validates :last_name, presence: true

• Validations can be checked on the controller side via the .valid? method.

Validations Code-Along

• We will be working together to add a few validations to our user manager system.
• We will also be looking at how to handle validation errors to create a nice user experience.

Validations Lab

• In this lab we will take what we learned about validations and apply it to the book manager application.
• Try out some of the validation methods to make sure the data entered in your book application is in the correct format.

Introduction to Database Associations

• More often than not, data within your database will be relational.
• What that means is that each piece relates to one another and can be accessed in series.
• For example: Imagine you have two tables - users and blog posts. If your data is relational you should be able to pull all blog posts related to a specific user.
• The most common association is a has many, belongs to relationship.

user.rb

class User < ActiveRecord::Base
	has_many :pets
end

pet.rb

class Pet < ActiveRecord::Base
	belongs_to :user
end

Associations Code-Along

• In this code-along we will be adding a Pet model to our user manager system.
• We will make it so that users own pets and pets belong to a specific user.
• We will also be creating views to see pets related to users.
• We will also see how we can represent this association in our routes with nested resources:

resources :users do
	resources :pets
end

Homework

• For homework you will be adding associations to your book manager application.
• Your goal is to link your book list with stores that sell the book.
• You will need to create a Store model with the appropriate attributes.
• Your app should have the ability to add stores to a specific book via a form.
• Don't worry about associating multiple stores with multiple books. Just one book to one store. Otherwise, this would be a more complex association called a many-to-many.