w3_d4_validations.md

Validations

So far, we've not been checking for whether or not the values that users have been entering in forms have been valid for our needs.

Checking that model attributes are within the bounds we want for saving in the database is called "validation".

Create an app to play in

  rails new validations_app
  cd validations_app

  rails g model Customer name:string email:string password:string age:integer active:boolean
  rails g model Order customer:references value:decimal
  rails g model Invoice paid:boolean
  rake db:migrate

ActiveRecord objects either correspond to a DB row, or they've not been saved yet.

  cust = Customer.new(name: "John Doe")
  cust.new_record?
  cust.save
  cust.new_record?

Validations are run before a record is saved. If any validations fail, the object does not get saved to the database.

Some validations

presence

  # customer.rb
  validates :name, presence: true

length

  # customer.rb
  validates :name, length: { minimum: 2 } 
  validates :name, length: { maximum: 500 }
  validates :name, length: { in: 8..255 }

numericality

  # order.rb
  validates :value, numericality: true #integer and float
  validates :value, numericality: { only_integer: true } #only integer

Also allows for :greater_than, :less_than, :odd, :even, :equal, et al.

uniqeness

  validates :name, uniqueness: true

lots more besides

We're not going into them, they're in the api

Some AR methods do skip validations, but create, save, and update_attributes (and their bang alternatives) require validations to pass.

To skip manually you can pass the validate: false option:

c.save(validate: false)

To check manually without saving you can ask if an object is valid or invalid:

  cust.valid?
  cust.invalid?

Errors

Any errors from validations which fail are placed into the errors collection of each AR object.

  # customer.rb
  validates :name, presence: true

  c = Customer.new
  c.errors # also call `.class` and `.to_a`
  c.valid?
  c.errors # .to_a
  c.error.full_messages

  c.save
  c.save!
  c.name = "gimme a name"

  c.save

Conditionally validating

Sometimes we only want to validate if certain conditions are met, and the validations can take options for :if and :unless:

  # with symbol for method
  class Order < ActiveRecord::Base
    validates :card_number, presence: true, if: :paid_with_card?
   
    def paid_with_card?
      payment_type == "card"
    end
  end

  # with Proc
  class Customer < ActiveRecord::Base
    attr_accessor :password_confirmation

    validates :password, confirmation: true, unless: Proc.new { |u| u.password.blank? }
    # validates :password, confirmation: true, unless: -> (u) { u.password.blank? } # this is and alternate proc syntax
  end

We can also specify when the validation should take place - whether the record needs create/update/save (defaults to 'save')

  class Customer < ActiveRecord::Base
    # it will be possible to update email with a duplicated value
    validates :email, uniqueness: true, on: :create
   
    # it will be possible to create the record with a non-numerical age
    validates :age, numericality: true, on: :update
   
    # the default (validates on both create and update)
    validates :name, presence: true, on: :save
  end

Custom Validation

Write your own methods to verify the state of your objects.

  class Order < ActiveRecord::Base
    validate :active_customer, on: :create
   
    def active_customer
      errors.add(:customer_id, "is not active") unless customer.active?
    end
  end

Add errors to attributes of the model or to the 'base' to cause the validations to fail, and to interrupt the save/create/update.

Exercise

Let's create a blog site which has Articles that can be commented on.

  rails new validations_exercise
  cd validations_exercise
  rails g model Article author_name:string title:string body:text
  rails g model Comment author_name:string article:references body:text
  rake db:migrate
  rails c

1. Write validations to check that an Article object must have both a title and a body.
2. Validate that a Comment has a body of less than 250 characters.
3. Validate that neither articles nor comments have the word "drupal" in their body.
4. Validate that a comment must have an associated article.
5. Validate that no author comments on their own article.

http://guides.rubyonrails.org/v4.1.8/active_record_validations.html

[i]: Exercise answers: class Article < ActiveRecord::Base validates :title, presence: true validates :body, presence: true validate :doesnt_mention_drupal private def doesnt_mention_drupal errors.add(:body, "must not mention drupal") if body.to_s.match('drupal') end end class Comment < ActiveRecord::Base belongs_to :article validates :body, length: { maximum: 250 } validates :article, presence: true validate :not_author_of_article validate :doesnt_mention_drupal private def not_author_of_article errors.add(:base, "mustn't comment on own article") if author_name && article.try(:author_name)==author_name end private def doesnt_mention_drupal errors.add(:body, "must not mention drupal") if body.to_s.match('drupal') end end