trgm.rb

require 'active_record'
require 'open-uri'
require 'pg'
require 'minitest/autorun'

ActiveRecord::Base.establish_connection(
  adapter: 'postgresql',
  database: 'trgm',
  host: 'localhost',
  username: 'postgres'
)

class Country < ActiveRecord::Base
  def self.similar(query)
    sql = %(
      SELECT name, similarity(name, '#{query}') AS s_name
      FROM countries WHERE name % '#{query}'
      ORDER BY s_name desc
    )
    connection.query(sql)
  end
end

class CreateCountryTable < ActiveRecord::Migration
  def self.up
    create_table :countries do |t|
      t.string :name
    end

    data = JSON.load open("http://api.vk.com/method/database.getCountries?v=5.34&need_all=1&count=234&lang=ru")
    data["response"]["items"].each do |country|
      Country.create!(name: country["title"])
    end

    enable_extension "pg_trgm"
  end

  def self.down
    drop_table :countries
  end
end

CreateCountryTable.migrate(:up) unless ActiveRecord::Base.connection.table_exists? :countries

p "Country count: #{Country.count}"

Country.similar("мадивы").each do |country|
  p country.first + ": " + country.last
end

describe Country do
  it 'находит страну по точному названию' do
    data = Country.similar 'Россия'
    assert_equal data.count, 1
    assert_equal data.first[0], 'Россия'
    assert_equal data.first[1], '1'
  end

  it 'находит страну с ошибкой в названии' do
    data = Country.similar 'Росия'
    assert_equal data.count, 1
    assert_equal data.first[0], 'Россия'
    assert data.first[1].to_f < 1
  end
end