bulk_insert_helper.rb

module BulkInsertHelper
  extend ActiveSupport::Concern
  def insert_sql
    fill_time_stamps
    self.class.arel_table.
      create_insert.tap do |im| 
        im.insert(
          self.send(
            :arel_attributes_with_values_for_create,
            self.attribute_names
          )
        )
      end.to_sql    
  end
  
  def fill_time_stamps
    columns, time_now = self.class.columns_hash, Time.now      
    %w(created_at updated_at).each do |attr|
      # if time stamp field is present and not set
      if columns.key?(attr) && send("#{attr}?")
        send("#{attr}=", time_now)
      end 
    end  
  end
  
  class_methods do
    def bulk_insert(rows, batch_size=1000)
      transaction do
        rows.lazy.each_slice(batch_size) do |batch|
          batch_sql = batch.lazy.map do |row|
            new(row).insert_sql
          end.to_a.join(", ")
          connection.insert_sql(batch_sql)
        end
      end
    end
  end
end
ActiveRecord::Base.send(:include, BulkInsertHelper)

# rows = (1..15).map{|i| {name: "name-#{i}", code: "code-#{i}"}}
# Invitation.bulk_insert(rows)