Add bulk import functionality to Rails Active Record (add this file to config/initializers, call <model>.import!(array-of-record-hashes))

active_record.rb

class ActiveRecord::Base
  
  def self.import!(record_list)
    raise ArgumentError "record_list not an Array of Hashes" unless record_list.is_a?(Array) && record_list.all? {|rec| rec.is_a? Hash }
    return record_list if record_list.empty?

    (1..record_list.count).step(1000).each do |start|
      key_list, value_list = convert_record_list(record_list[start-1..start+999])
      sql = "INSERT INTO #{self.table_name} (#{key_list.join(", ")}) VALUES #{value_list.map {|rec| "(#{rec.join(", ")})" }.join(" ,")}"
      self.connection.insert_sql(sql)
    end
    
    return record_list
  end
  
  def self.convert_record_list(record_list)
    # Build the list of keys
    key_list = record_list.map(&:keys).flatten.map(&:to_s).uniq.sort

    value_list = record_list.map do |rec|
      list = []
      key_list.each {|key| list <<  ActiveRecord::Base.connection.quote(rec[key] || rec[key.to_sym]) }
      list
    end
    
    # If table has standard timestamps and they're not in the record list then add them to the record list
    time = ActiveRecord::Base.connection.quote(Time.now)
    for field_name in %w(created_at updated_at)
      if self.column_names.include?(field_name) && !(key_list.include?(field_name))
        key_list << field_name
        value_list.each {|rec| rec << time }
      end
    end
    
    return [key_list, value_list]
  end
end

I think this code double-includes some rows. Why start at 1 and then go from start-1 to start+999? This means your first range is from 0..1000, then 1000..2000, so you include row 1000 twice. How about something more like this: (0...record_list.count).step(1000).each do |start| and then record_list[start...start+1000]}

You are indeed double-including counting rows...
Try:
(0..record_list.count).step(1000).each do |start| key_list, value_list = convert_record_list(record_list[start..(start+999)])

You are forgetting to use default values if they are set, instead you would just set it to 'NULL'

I added:

default = columns.map { |c| [c.name, c.default] }.to_h
default['created_at'] = Time.now.utc
default['updated_at'] = Time.now.utc

and modified the line :
key_list.each { |key| list << ActiveRecord::Base.connection.quote(rec[key] || rec[key.to_sym] || default[key]) }

I honestly disagree with baking in the step functionality to that method anyways. Why should that method care about doing anything but preparing the bulk insert statement? It shouldn't be throttling the input, the user shouldn't be passing things to it that slow it down, and if they do, they should be adjusting their input size.

The cleaner implementation is to avoid adding that logic into the method in the first place, for all those suggesting he simply fix the resulting logic bug.

@jackrg how might you write this if you wanted to selectively insert columns from your raw data (e.g. in a csv, say you only want column 1, 3, and 4 to save to your ActiveRecord table instead of all columns 1-4)? I know how to do that using CSV.foreach, but it's taking 5 minutes to import 20,000 rows.

This is vulnerable to sql injection - you need to escape values!