Ruby on Rails - Import Data from a CSV file

Question

I would like to import data from a CSV file into an existing database table. I do not want to save the CSV file, just take the data from it and put it into the existing table. I am using Ruby 1.9.2 and Rails 3.

This is my table:

create_table "mouldings", :force => true do |t|
  t.string   "suppliers_code"
  t.datetime "created_at"
  t.datetime "updated_at"
  t.string   "name"
  t.integer  "supplier_id"
  t.decimal  "length",         :precision => 3, :scale => 2
  t.decimal  "cost",           :precision => 4, :scale => 2
  t.integer  "width"
  t.integer  "depth"
end

Can you give me some code to show me the best way to do this, thanks.

Answer 1

The smarter_csv gem was specifically created for this use-case: to read data from CSV file and quickly create database entries.

  require 'smarter_csv'
  options = {}
  SmarterCSV.process('input_file.csv', options) do |chunk|
    chunk.each do |data_hash|
      Moulding.create!( data_hash )
    end
  end

You can use the option chunk_size to read N csv-rows at a time, and then use Resque in the inner loop to generate jobs which will create the new records, rather than creating them right away - this way you can spread the load of generating entries to multiple workers.

See also: https://github.com/tilo/smarter_csv

Answer 2

This can help. It has code examples too:

http://csv-mapper.rubyforge.org/

Or for a rake task for doing the same:

http://erikonrails.snowedin.net/?p=212

Answer 3

It is better to wrap the database related process inside a transaction block. Code snippet blow is a full process of seeding a set of languages to Language model,

require 'csv'

namespace :lan do
  desc 'Seed initial languages data with language & code'
  task init_data: :environment do
    puts '>>> Initializing Languages Data Table'
    ActiveRecord::Base.transaction do
      csv_path = File.expand_path('languages.csv', File.dirname(__FILE__))
      csv_str = File.read(csv_path)
      csv = CSV.new(csv_str).to_a
      csv.each do |lan_set|
        lan_code = lan_set[0]
        lan_str = lan_set[1]
        Language.create!(language: lan_str, code: lan_code)
        print '.'
      end
    end
    puts ''
    puts '>>> Languages Database Table Initialization Completed'
  end
end

Snippet below is a partial of languages.csv file,

aa,Afar
ab,Abkhazian
af,Afrikaans
ak,Akan
am,Amharic
ar,Arabic
as,Assamese
ay,Aymara
az,Azerbaijani
ba,Bashkir
...

Answer 4

It's better to use CSV::Table and use String.encode(universal_newline: true). It converting CRLF and CR to LF

Answer 5

Simpler version of yfeldblum's answer, that is simpler and works well also with large files:

require 'csv'    

CSV.foreach(filename, :headers => true) do |row|
  Moulding.create!(row.to_hash)
end

No need for with_indifferent_access or symbolize_keys, and no need to read in the file to a string first.

It doesnt't keep the whole file in memory at once, but reads in line by line and creates a Moulding per line.

Answer 6

The better way is to include it in a rake task. Create import.rake file inside /lib/tasks/ and put this code to that file.

desc "Imports a CSV file into an ActiveRecord table"
task :csv_model_import, [:filename, :model] => [:environment] do |task,args|
  lines = File.new(args[:filename], "r:ISO-8859-1").readlines
  header = lines.shift.strip
  keys = header.split(',')
  lines.each do |line|
    values = line.strip.split(',')
    attributes = Hash[keys.zip values]
    Module.const_get(args[:model]).create(attributes)
  end
end

After that run this command in your terminal rake csv_model_import[file.csv,Name_of_the_Model]