gistfile1.rb

class Category < ActiveRecord::Base

  validates :name, presence: true, :uniqueness => true

  has_many :articles

end


cLoading development environment (Rails 3.2.8)
[1] pry(main)> ct = Category.new(name: '')
=> #<Category id: nil, name: "", created_at: nil, updated_at: nil>
[2] pry(main)> ct.valid?
  Category Exists (0.2ms)  SELECT 1 AS one FROM `categories` WHERE `categories`.`name` = BINARY '' LIMIT 1
=> false
[3] pry(main)> ct = Category.new(name: 'Новости')
=> #<Category id: nil, name: "Новости", created_at: nil, updated_at: nil>
[4] pry(main)> ct.valid?
  Category Exists (0.3ms)  SELECT 1 AS one FROM `categories` WHERE `categories`.`name` = BINARY 'Новости' LIMIT 1
=> true
[5] pry(main)> ct = Category.new(name: Category.first.name)
  Category Load (0.2ms)  SELECT `categories`.* FROM `categories` LIMIT 1
=> #<Category id: nil, name: "Новости", created_at: nil, updated_at: nil>
[6] pry(main)> ct.valid?
  Category Exists (0.3ms)  SELECT 1 AS one FROM `categories` WHERE `categories`.`name` = BINARY 'Новости' LIMIT 1
=> true