How I do CSV imports with postgres & rails

csv_import.rb

class CsvImport
  include ActiveRecord::Sanitization::ClassMethods
  attr_accessor :connection, :header

  def self.read_csv(file)
    file.is_a?(Array) ? file : file.read.encode(newline: :universal).lines
  end

  def initialize(connection, csv_lines, table_name)
    @connection, @table_name = connection, table_name
    @header, *@file = csv_lines
    letters = (97..122).map(&:chr).shuffle
    # Unique suffix
    @table_name += "__" + letters[1..10].join
  end

  def check_header_row(expected)
    req_header_row = @header.strip.split(",")
    raise "Expected header to be #{expected} but it was #{req_header_row}" if req_header_row != expected
  end

  def schema(options={})
    @connection.create_table(
      @table_name,
      {temporary: true}.merge(options)
    ) do |t|
      yield(t)
    end
  end

  def prepare_data
    import!
    yield klass
  end

  def validate_data
    import!
    yield klass
  end

  def after
    import!
    yield klass
  end

  def klass
    return @klass if @klass
    @klass = make_klass
  end

  def make_klass
    tn = @table_name
    Class.new(ApplicationRecord) do
      self.table_name = tn
    end
  end

  def import!
    return if @imported
    @imported = true
    i = 2 # row number
    @connection.raw_connection.copy_data <<-SQL do
      copy #{@table_name} from stdin with csv delimiter ',' quote '"'
    SQL
      @file.each do |line|
        @connection.raw_connection.put_copy_data i.to_s + "," + line
        i += 1
      end
    end
  end

  def teardown!
    @connection.drop_table(@table_name)
  end

  def self.import(connection, file, table_name = csv_imports)
    instance = new(connection, file, table_name)
    connection.transaction do
      yield(instance)
      instance.teardown!
    end
  end
end

foo_bar.rb

class FooBar < ApplicationRecord
  def self.import_from_csv(csv_lines)
    CsvImport.import(ApplicationRecord.connection, csv_lines, 'tmp_upload_thingy') do |import|
      req_header_row = import.header.strip.split(",")
      raise "Expected header to start with #{csv_headers} but it was #{req_header_row}" if req_header_row[0..(csv_headers.length-1)] != csv_headers

      import.schema do |t|
        t.string :name
        t.string :kind
        (req_header_row.length - csv_headers.length).times do |i|
          t.string "col_#{i}"
        end
      end

      import.import!

      import.klass.connection.execute <<-SQL
        insert into foo_bars (
          name,
          type,
        ) select
          name,
          kind,
        from #{import.klass.table_name}
      SQL
    end
  end
end