thingy_csv_export.rb

class ThingyExporter
  SQL_QUERY_PATH = Rails.root.join("app/services/thingy_exporter/query.sql")
  SQL_QUERY = File.read(SQL_QUERY_PATH)

  HEADERS = %w[
    thingy_id
    tag_id
    thingy_filename
    survey_question_token
    tag_name
    tag_number
    quote
    start_char
    end_char
    tagger
    tagtime
  ].freeze

  def initialize(thingy)
    @thingy = thingy
    @name = thingy.name.parameterize
  end

  def export
    log "Start DB query"

    pg_conn = ActiveRecord::Base.connection.raw_connection # :: PG::Connection
    pg_result = pg_conn.exec_params(SQL_QUERY, [@thingy.id]) # :: PG::Result

    log "Start generating CSV"

    csv_data = CSV.generate(encoding: "UTF-8", headers: HEADERS, write_headers: true, force_quotes: true) do |csv|
      pg_result.each do |result_hash|
        csv << result_hash
      end
    end

    log "Finished generating CSV"
    csv_data
  ensure
    # Clear the memory associated with the PG::Result
    log "Cleaning up PG::Result memory"
    pg_result.clear if pg_result
  end

  def log(msg)
    Rails.logger.info("ThingyExporter: #{msg}")
  end
end