Reducing the amount of database queries on create

Currently I'm working on an application that has to parse a large XML file and use the data inside of it to create entities in the database. The code for creating the entities is the following part of the a controller call:

def create
    parser = EuroPassVacancy.new params[:vacancy][:file].tempfile.path
    ids = parser.collect_vacancy_ids
    ids.each do |vacancy_id|
      country = Country.find_or_create_by_code(:code => parser.country_code(vacancy_id), :name => parser.country_code(vacancy_id))
      company = Company.find_or_create_by_name(:name => parser.employer_name(vacancy_id), :address => parser.employer_address(vacancy_id),
                                                  :contact => parser.employer_contact(vacancy_id), :phone => parser.employer_phone(vacancy_id),
                                                  :email => parser.employer_email(vacancy_id), :fax => parser.employer_fax(vacancy_id),
                                                  :country => country)
      Vacancy.create(:pes_id => parser.pes_id(vacancy_id), :title => parser.title(vacancy_id), :description => parser.description(vacancy_id),
                     :country => country, :region_code => parser.region_code(vacancy_id), :company_id => company, :isco_code => parser.isco_code(vacancy_id),
                     :nace_code => parser.nace_code(vacancy_id))
    end
    redirect_to :action => :index
  end

It's a pretty heavy loop, but i'm reasonably confident that the parsing is going ok. What currently bothers me is the amount of queries beeing generated for each create statement. Below is a small copy of 2 insert statement of Vacancies:

AREL (0.0ms)  INSERT INTO `vacancies` (`country_id`, `pes_id`, `title`, `region_code`, `isco_code`, `created_at`, `updated_at`, `description`, `company_id`, `na开发者_运维知识库ce_code`) VALUES (9, 50, 'Konstruktér strojní, StrojírenÅ¡tí technici projektanti, konstruktéři', 'RL041', 3118, '2011-05-25 13:19:16', '2011-05-25 13:19:16', 'ÚSO - strojní. Konstrukce nástrojů na tváření a lisování kovů, forem na lisování plastů. Znalost tech. a právních norem, ISO 9001, 14001 souvisejících s výrobním programem v rozsahu potÅ™ebném pro vývoj produktu a konstrukci výrobních prostÅ™edků - lisování a tváření kovů, plastů, montážních přípravků, PC - konstrukÄ�ní SW - CAD, 3-D (Solid Edge výhodou), OFFICE Outlook, NJ/AJ uživatelská úroveň, ŘP sk. B.', 1, 0)
  SQL (31.2ms)  COMMIT
  Country Load (0.0ms)  SELECT `countries`.* FROM `countries` WHERE `countries`.`code` = 'cy' LIMIT 1
  SQL (0.0ms)  BEGIN
  AREL (0.0ms)  INSERT INTO `countries` (`updated_at`, `name`, `code`, `created_at`) VALUES ('2011-05-25 13:19:18', 'cy', 'cy', '2011-05-25 13:19:18')
  SQL (63.0ms)  COMMIT
  Company Load (0.0ms)  SELECT `companies`.* FROM `companies` WHERE `companies`.`name` = 'ΚΛΕΙΤΟΣ ΓΕΩΡΓΙΟΥ & ΥΙΟΣ ΛΙΜΙΤΕΔ' LIMIT 1
  SQL (0.0ms)  BEGIN
  SQL (0.0ms)  SELECT 1 FROM `companies` WHERE `companies`.`name` = 'ΚΛΕΙΤΟΣ ΓΕΩΡΓΙΟΥ & ΥΙΟΣ ΛΙΜΙΤΕΔ' AND `companies`.`country_id` = 10 AND (`companies`.`name` = BINARY 'ΚΛΕΙΤΟΣ ΓΕΩΡΓΙΟΥ & ΥΙΟΣ ΛΙΜΙΤΕΔ') LIMIT 1
  SQL (0.0ms)  ROLLBACK
  SQL (0.0ms)  BEGIN
  SQL (0.0ms)  ROLLBACK
  Country Load (0.0ms)  SELECT `countries`.* FROM `countries` WHERE `countries`.`code` = 'cy' LIMIT 1
  Company Load (0.0ms)  SELECT `companies`.* FROM `companies` WHERE `companies`.`name` = 'ΠΑ�ΙΚΚΟΣ ΠΙΣΣΟΥΡΙΟΣ ΚΑΙ ΑΔΕΛΦΟΣ ΚΟ ΛΤΔ' LIMIT 1
  SQL (0.0ms)  BEGIN
  SQL (15.6ms)  SELECT 1 FROM `companies` WHERE `companies`.`name` = 'ΠΑ�ΙΚΚΟΣ ΠΙΣΣΟΥΡΙΟΣ ΚΑΙ ΑΔΕΛΦΟΣ ΚΟ ΛΤΔ' AND `companies`.`country_id` = 10 AND (`companies`.`name` = BINARY 'ΠΑ�ΙΚΚΟΣ ΠΙΣΣΟΥΡΙΟΣ ΚΑΙ ΑΔΕΛΦΟΣ ΚΟ ΛΤΔ') LIMIT 1
  SQL (0.0ms)  ROLLBACK
  SQL (0.0ms)  BEGIN
  SQL (0.0ms)  ROLLBACK
  CACHE (0.0ms)  SELECT `countries`.* FROM `countries` WHERE `countries`.`code` = 'cy' LIMIT 1
  Company Load (0.0ms)  SELECT `companies`.* FROM `companies` WHERE `companies`.`name` = 'THE DELHI PALACE INDIAN RESTAURANT LTD' LIMIT 1
  SQL (0.0ms)  BEGIN
  SQL (0.0ms)  SELECT 1 FROM `companies` WHERE `companies`.`name` = 'THE DELHI PALACE INDIAN RESTAURANT LTD' AND `companies`.`country_id` = 10 AND (`companies`.`name` = BINARY 'THE DELHI PALACE INDIAN RESTAURANT LTD') LIMIT 1
  SQL (0.0ms)  ROLLBACK
  SQL (0.0ms)  BEGIN
  SQL (0.0ms)  ROLLBACK
  CACHE (0.0ms)  SELECT `countries`.* FROM `countries` WHERE `countries`.`code` = 'cy' LIMIT 1
  Company Load (0.0ms)  SELECT `companies`.* FROM `companies` WHERE `companies`.`name` = 'EURES ADVISOR , STELLA PAPADOPOULOU APPIOU' LIMIT 1
  SQL (0.0ms)  BEGIN
  SQL (0.0ms)  SELECT 1 FROM `companies` WHERE `companies`.`name` = 'EURES ADVISOR , STELLA PAPADOPOULOU APPIOU' AND `companies`.`country_id` = 10 AND (`companies`.`name` = BINARY 'EURES ADVISOR , STELLA PAPADOPOULOU APPIOU') LIMIT 1
  AREL (0.0ms)  INSERT INTO `companies` (`email`, `phone`, `country_id`, `created_at`, `address`, `contact`, `fax`, `updated_at`, `name`) VALUES ('sappiou@dl.mlsi.gov.cy', '00357 22 403000', 10, '2011-05-25 13:20:13', 'MOUSEIOU STREET 3 1102 , ΛΕΥΚΩΣΙΑ', 'STELLA PAPADOPOULOU APPIOU', '00357 22 873170/1', '2011-05-25 13:20:13', 'EURES ADVISOR , STELLA PAPADOPOULOU APPIOU')
  SQL (31.2ms)  COMMIT
  SQL (0.0ms)  BEGIN
  SQL (0.0ms)  ROLLBACK
  Country Load (0.0ms)  SELECT `countries`.* FROM `countries` WHERE `countries`.`code` = 'cy' LIMIT 1
  Company Load (0.0ms)  SELECT `companies`.* FROM `companies` WHERE `companies`.`name` = 'EURES ASSISTANT , NORA LANDA' LIMIT 1
  SQL (0.0ms)  BEGIN
  SQL (0.0ms)  SELECT 1 FROM `companies` WHERE `companies`.`name` = 'EURES ASSISTANT , NORA LANDA' AND `companies`.`country_id` = 10 AND (`companies`.`name` = BINARY 'EURES ASSISTANT , NORA LANDA') LIMIT 1
  AREL (0.0ms)  INSERT INTO `companies` (`email`, `phone`, `country_id`, `created_at`, `address`, `contact`, `fax`, `updated_at`, `name`) VALUES ('nlanda@dl.mlsi.gov.cy', '00357 25 827327', 10, '2011-05-25 13:20:29', '67 FRANKLIN ROOSEVELT AV 3011 , ΛΕΜΕΣΟΣ', 'NOT AVAILABLE', '00357 25 306563', '2011-05-25 13:20:29', 'EURES ASSISTANT , NORA LANDA')
  SQL (31.2ms)  COMMIT
  SQL (0.0ms)  BEGIN
  SQL (0.0ms)  ROLLBACK
  Country Load (0.0ms)  SELECT `countries`.* FROM `countries` WHERE `countries`.`code` = 'cy' LIMIT 1
  Company Load (0.0ms)  SELECT `companies`.* FROM `companies` WHERE `companies`.`name` = 'ΕΛΕ�Α ΤΖΙΟΒΑ�Η' LIMIT 1
  SQL (0.0ms)  BEGIN
  SQL (0.0ms)  SELECT 1 FROM `companies` WHERE `companies`.`name` = 'ΕΛΕ�Α ΤΖΙΟΒΑ�Η' AND `companies`.`country_id` = 10 AND (`companies`.`name` = BINARY 'ΕΛΕ�Α ΤΖΙΟΒΑ�Η') LIMIT 1
  AREL (0.0ms)  INSERT INTO `companies` (`email`, `phone`, `country_id`, `created_at`, `address`, `contact`, `fax`, `updated_at`, `name`) VALUES ('georgiam85@hotmail.com', '0035723833780', 10, '2011-05-25 13:20:45', 'ΔΑΦ�ΗΣ 11-13 5314 AMMOHOSTOS', 'MRS GEORGIA MASIA', '0035723833177', '2011-05-25 13:20:45', 'ΕΛΕ�Α ΤΖΙΟΒΑ�Η')
  SQL (31.2ms)  COMMIT
  SQL (0.0ms)  BEGIN
  SQL (0.0ms)  ROLLBACK
  Country Load (0.0ms)  SELECT `countries`.* FROM `countries` WHERE `countries`.`code` = 'cy' LIMIT 1
  Company Load (0.0ms)  SELECT `companies`.* FROM `companies` WHERE `companies`.`name` = 'EURES ADVISOR , MINAS HADJICONSTANTI' LIMIT 1
  SQL (0.0ms)  BEGIN
  SQL (0.0ms)  SELECT 1 FROM `companies` WHERE `companies`.`name` = 'EURES ADVISOR , MINAS HADJICONSTANTI' AND `companies`.`country_id` = 10 AND (`companies`.`name` = BINARY 'EURES ADVISOR , MINAS HADJICONSTANTI') LIMIT 1
  AREL (0.0ms)  INSERT INTO `companies` (`email`, `phone`, `country_id`, `created_at`, `address`, `contact`, `fax`, `updated_at`, `name`) VALUES ('mhadjiconstanti@dl.mlsi.gov.cy', '00357 24 805328', 10, '2011-05-25 13:21:01', 'P.O.BOX 40136 6301 , ΛΑΡ�ΑΚΑ', 'MINAS HADJICONSTANTI', '00357 24 304532', '2011-05-25 13:21:01', 'EURES ADVISOR , MINAS HADJICONSTANTI')
  SQL (62.4ms)  COMMIT
  SQL (0.0ms)  BEGIN
  SQL (1.0ms)  ROLLBACK
  Country Load (0.0ms)  SELECT `countries`.* FROM `countries` WHERE `countries`.`code` = 'it' LIMIT 1
  Company Load (0.0ms)  SELECT `companies`.* FROM `companies` WHERE `companies`.`name` = 'SAILER ANDREAS' LIMIT 1
  SQL (0.0ms)  BEGIN
  SQL (0.0ms)  SELECT 1 FROM `companies` WHERE `companies`.`name` = 'SAILER ANDREAS' AND `companies`.`country_id` = 8 AND (`companies`.`name` = BINARY 'SAILER ANDREAS') LIMIT 1
  AREL (0.0ms)  INSERT INTO `companies` (`email`, `phone`, `country_id`, `created_at`, `address`, `contact`, `fax`, `updated_at`, `name`) VALUES ('info@asailer.it', '+39-0471-932632', 8, '2011-05-25 13:21:18', 'A.Duerer-Str. 20 - Via Duerer 20 39100-Bozen - Bolzano', 'Giulia Morello', '+39-0471-932691', '2011-05-25 13:21:18', 'SAILER ANDREAS')
  SQL (30.0ms)  COMMIT
  SQL (0.0ms)  BEGIN
  AREL (0.0ms)  INSERT INTO `vacancies` (`country_id`, `pes_id`, `title`, `region_code`, `isco_code`, `created_at`, `updated_at`, `description`, `company_id`, `nace_code`) VALUES (8, 64, 'ricerca di ingegnere e architetto per studio di ingegneria', 'R3311', 4190, '2011-05-25 13:21:24', '2011-05-25 13:21:24', 'Studio di ingegneria cerca, anche per subito, un ingegnere e un architetto, per la progettazione architettonica e strutturale, stima e contabilità di opere, il tutto nel settore delle costruzioni civili e delle opere speciali . E\' richiesta ottima conoscenza di autocad, pacchetto office e programmi di strutture e contabilità. Sede di lavoro: Bolzano centro: si chiede gentilmente che venga inviato un curriculum professionale con foto allegata.', 1, 74)
  SQL (62.4ms)  COMMIT

There seems to be ALOT more select queries for the countries & companies going on than I'd like to have. I was wondering if an optimalization can be done about the code to reduce these queries.

The simplest way to crack this is to cache the lookups or creations you perform. For instance, you're selecting the same country over and over again which is, as you've identified, wasteful.

You can do this by defining a helper method:

class Country < ActiveRecord::Base
  def self.resolve_country(options)
    @resolved_countries ||= { }

    @resolved_countries[options[:code]] ||= Country.find_or_create_by_code(options)
  end
end

This will load your country only once and if this pattern is applied to other models it should significantly speed up your loading.

One thing to keep in mind is when you may need to reset these caches for testing purposes. Adding a method to do this is always a good idea, and isn't hard:

def self.reset_cache!
  @resolved_countries = nil
end

This can be put in your setup method for your model's unit tests.