Guides.rubyonrails.org

class Person < ActiveRecord::Base
  validates :name, presence: true
end

Person.create(name: "John Doe").valid? # => true
Person.create(name: nil).valid? # => false

class Person < ActiveRecord::Base
end

$ rails console
>> p = Person.new(name: "John Doe")
=> #<Person id: nil, name: "John Doe", created_at: nil, updated_at: nil>
>> p.new_record?
=> true
>> p.save
=> true
>> p.new_record?
=> false

class Person < ActiveRecord::Base
  validates :name, presence: true
end

Person.create(name: "John Doe").valid? # => true
Person.create(name: nil).valid? # => false

class Person < ActiveRecord::Base
  validates :name, presence: true
end

>> p = Person.new
# => #<Person id: nil, name: nil>
>> p.errors.messages
# => {}

>> p.valid?
# => false
>> p.errors.messages
# => {name:["can't be blank"]}

>> p = Person.create
# => #<Person id: nil, name: nil>
>> p.errors.messages
# => {name:["can't be blank"]}

>> p.save
# => false

>> p.save!
# => ActiveRecord::RecordInvalid: Validation failed: Name can't be blank

>> Person.create!
# => ActiveRecord::RecordInvalid: Validation failed: Name can't be blank

class Person < ActiveRecord::Base
  validates :name, presence: true
end

>> Person.new.errors[:name].any? # => false
>> Person.create.errors[:name].any? # => true

class Person < ActiveRecord::Base
  validates :terms_of_service, acceptance: true
end

class Person < ActiveRecord::Base
  validates :terms_of_service, acceptance: { accept: 'yes' }
end

class Library < ActiveRecord::Base
  has_many :books
  validates_associated :books
end

class Person < ActiveRecord::Base
  validates :email, confirmation: true
end

<%= text_field :person, :email %>
<%= text_field :person, :email_confirmation %>

class Person < ActiveRecord::Base
  validates :email, confirmation: true
  validates :email_confirmation, presence: true
end

class Account < ActiveRecord::Base
  validates :subdomain, exclusion: { in: %w(www us ca jp),
    message: "%{value} is reserved." }
end

class Product < ActiveRecord::Base
  validates :legacy_code, format: { with: /\A[a-zA-Z]+\z/,
    message: "only allows letters" }
end

class Coffee < ActiveRecord::Base
  validates :size, inclusion: { in: %w(small medium large),
    message: "%{value} is not a valid size" }
end

class Person < ActiveRecord::Base
  validates :name, length: { minimum: 2 }
  validates :bio, length: { maximum: 500 }
  validates :password, length: { in: 6..20 }
  validates :registration_number, length: { is: 6 }
end

class Person < ActiveRecord::Base
  validates :bio, length: { maximum: 1000,
    too_long: "%{count} characters is the maximum allowed" }
end

class Essay < ActiveRecord::Base
  validates :content, length: {
    minimum: 300,
    maximum: 400,
    tokenizer: lambda { |str| str.scan(/\w+/) },
    too_short: "must have at least %{count} words",
    too_long: "must have at most %{count} words"
  }
end

/\A[+-]?\d+\Z/

class Player < ActiveRecord::Base
  validates :points, numericality: true
  validates :games_played, numericality: { only_integer: true }
end

class Person < ActiveRecord::Base
  validates :name, :login, :email, presence: true
end

class LineItem < ActiveRecord::Base
  belongs_to :order
  validates :order, presence: true
end

class Order < ActiveRecord::Base
  has_many :line_items, inverse_of: :order
end

class Person < ActiveRecord::Base
  validates :name, :login, :email, absence: true
end

class LineItem < ActiveRecord::Base
  belongs_to :order
  validates :order, absence: true
end

class Order < ActiveRecord::Base
  has_many :line_items, inverse_of: :order
end

class Account < ActiveRecord::Base
  validates :email, uniqueness: true
end

class Holiday < ActiveRecord::Base
  validates :name, uniqueness: { scope: :year,
    message: "should happen once per year" }
end

class Person < ActiveRecord::Base
  validates :name, uniqueness: { case_sensitive: false }
end

class GoodnessValidator < ActiveModel::Validator
  def validate(record)
    if record.first_name == "Evil"
      record.errors[:base] << "This person is evil"
    end
  end
end

class Person < ActiveRecord::Base
  validates_with GoodnessValidator
end

class GoodnessValidator < ActiveModel::Validator
  def validate(record)
    if options[:fields].any?{|field| record.send(field) == "Evil" }
      record.errors[:base] << "This person is evil"
    end
  end
end

class Person < ActiveRecord::Base
  validates_with GoodnessValidator, fields: [:first_name, :last_name]
end

class Person < ActiveRecord::Base
  validate do |person|
    GoodnessValidator.new(person).validate
  end
end

class GoodnessValidator
  def initialize(person)
    @person = person
  end

  def validate
    if some_complex_condition_involving_ivars_and_private_methods?
      @person.errors[:base] << "This person is evil"
    end
  end

  # ...
end

class Person < ActiveRecord::Base
  validates_each :name, :surname do |record, attr, value|
    record.errors.add(attr, 'must start with upper case') if value =~ /\A[a-z]/
  end
end

class Coffee < ActiveRecord::Base
  validates :size, inclusion: { in: %w(small medium large),
    message: "%{value} is not a valid size" }, allow_nil: true
end

class Topic < ActiveRecord::Base
  validates :title, length: { is: 5 }, allow_blank: true
end

Topic.create(title: "").valid?  # => true
Topic.create(title: nil).valid? # => true

class Person < 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
end

class Person < ActiveRecord::Base
  validates :name, presence: { strict: true }
end

Person.new.valid?  # => ActiveModel::StrictValidationFailed: Name can't be blank

class Person < ActiveRecord::Base
  validates :token, presence: true, uniqueness: true, strict: TokenGenerationException
end

Person.new.valid?  # => TokenGenerationException: Token can't be blank

class Order < ActiveRecord::Base
  validates :card_number, presence: true, if: :paid_with_card?

  def paid_with_card?
    payment_type == "card"
  end
end

class Person < ActiveRecord::Base
  validates :surname, presence: true, if: "name.nil?"
end

class Account < ActiveRecord::Base
  validates :password, confirmation: true,
    unless: Proc.new { |a| a.password.blank? }
end

class User < ActiveRecord::Base
  with_options if: :is_admin? do |admin|
    admin.validates :password, length: { minimum: 10 }
    admin.validates :email, presence: true
  end
end

class Computer < ActiveRecord::Base
  validates :mouse, presence: true,
                    if: ["market.retail?", :desktop?]
                    unless: Proc.new { |c| c.trackpad.present? }
end

class MyValidator < ActiveModel::Validator
  def validate(record)
    unless record.name.starts_with? 'X'
      record.errors[:name] << 'Need a name starting with X please!'
    end
  end
end

class Person
  include ActiveModel::Validations
  validates_with MyValidator
end

class EmailValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    unless value =~ /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i
      record.errors[attribute] << (options[:message] || "is not an email")
    end
  end
end

class Person < ActiveRecord::Base
  validates :email, presence: true, email: true
end

class Invoice < ActiveRecord::Base
  validate :expiration_date_cannot_be_in_the_past,
    :discount_cannot_be_greater_than_total_value

  def expiration_date_cannot_be_in_the_past
    if expiration_date.present? && expiration_date < Date.today
      errors.add(:expiration_date, "can't be in the past")
    end
  end

  def discount_cannot_be_greater_than_total_value
    if discount > total_value
      errors.add(:discount, "can't be greater than total value")
    end
  end
end

class Invoice < ActiveRecord::Base
  validate :active_customer, on: :create

  def active_customer
    errors.add(:customer_id, "is not active") unless customer.active?
  end
end

class Person < ActiveRecord::Base
  validates :name, presence: true, length: { minimum: 3 }
end

person = Person.new
person.valid? # => false
person.errors.messages
 # => {:name=>["can't be blank", "is too short (minimum is 3 characters)"]}

person = Person.new(name: "John Doe")
person.valid? # => true
person.errors.messages # => {}

class Person < ActiveRecord::Base
  validates :name, presence: true, length: { minimum: 3 }
end

person = Person.new(name: "John Doe")
person.valid? # => true
person.errors[:name] # => []

person = Person.new(name: "JD")
person.valid? # => false
person.errors[:name] # => ["is too short (minimum is 3 characters)"]

person = Person.new
person.valid? # => false
person.errors[:name]
 # => ["can't be blank", "is too short (minimum is 3 characters)"]

class Person < ActiveRecord::Base
  def a_method_used_for_validation_purposes
    errors.add(:name, "cannot contain the characters !@#%*()_-+=")
  end
end

person = Person.create(name: "!@#")

person.errors[:name]
 # => ["cannot contain the characters !@#%*()_-+="]

person.errors.full_messages
 # => ["Name cannot contain the characters !@#%*()_-+="]

  class Person < ActiveRecord::Base
    def a_method_used_for_validation_purposes
      errors[:name] = "cannot contain the characters !@#%*()_-+="
    end
  end

  person = Person.create(name: "!@#")

  person.errors[:name]
   # => ["cannot contain the characters !@#%*()_-+="]

  person.errors.to_a
   # => ["Name cannot contain the characters !@#%*()_-+="]

class Person < ActiveRecord::Base
  def a_method_used_for_validation_purposes
    errors[:base] << "This person is invalid because ..."
  end
end

class Person < ActiveRecord::Base
  validates :name, presence: true, length: { minimum: 3 }
end

person = Person.new
person.valid? # => false
person.errors[:name]
 # => ["can't be blank", "is too short (minimum is 3 characters)"]

person.errors.clear
person.errors.empty? # => true

p.save # => false

p.errors[:name]
# => ["can't be blank", "is too short (minimum is 3 characters)"]

class Person < ActiveRecord::Base
  validates :name, presence: true, length: { minimum: 3 }
end

person = Person.new
person.valid? # => false
person.errors.size # => 2

person = Person.new(name: "Andrea", email: "andrea@example.com")
person.valid? # => true
person.errors.size # => 0

<% if @post.errors.any? %>
  <div id="error_explanation">
    <h2><%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:</h2>

    <ul>
    <% @post.errors.full_messages.each do |msg| %>
      <li><%= msg %></li>
    <% end %>
    </ul>
  </div>
<% end %>

<div class="field_with_errors">
 <input id="post_title" name="post[title]" size="30" type="text" value="">
</div>

.field_with_errors {
  padding: 2px;
  background-color: red;
  display: table;
}