geocoded_timestamp.rb

# add a db schema migration to add geocoded_at to listings
add_column :listings, :geocoded_at, :timestamp, default: nil

# add a geocoded? method to the model
class Listing < ApplicationRecord
  def geocoded?
    read_attribute(:geocoded) || geocoded_at.present?
  end
end

# write four unit tests for the above method, testing all four possible combinations of the two attributes.

# adjust the geocoding code (service) to only use that method to check for geocoding status

# add the data_migrate gem to the gemfile

# write a data migration to set geocoded_at to a fixed timestamp (same for all records) where geocoded=1.
# See https://github.com/ilyakatz/data-migrate for how to do this

# deploy, run schema and data migrations, and check that all was migrated correctly
  
# add migration to drop the unneccessary "geocoded" attribute from listings
remove_column :listings, :geocoded

# change the geocoded? method to only check for the timestamp (read_attribute(:geocoded) will raise an error)

# deploy & all good