Converting Serialized YAML to Serialized JSON in Rails models

model_json.rb

class Medium < ActiveRecord::Base
  serialize :payload, JSON
end

model_yaml.rb

class Medium < ActiveRecord::Base
  serialize :payload
end

rake_task_code.rb

# create a facade model to avoid validations and other shenanigans
faux_medium = Class.new ActiveRecord::Base
faux_medium.table_name = "media"

# only loading the id and the payload helps avoid certain problems and speeds up the conversion
faux_medium.select([:id, :payload]).find_in_batches do |media|
  media.each do |medium|
    begin

      # manually encode to JSON because of the facade class
      medium.payload = YAML.load(medium.send(:attribute, :payload)).to_json
      medium.save!

    rescue Exception => e
      puts "Could not fix medium #{medium.id} for #{e.message}"
    end
  end
end

test_parsers.rb

hash = { "A" => "B", "C" => "D", "E" => "F", "G" => "H", "I" => { "J" => "K", "L" => "M", "N" => "O", "P" => "Q", "R" => "S" } }
yaml = hash.to_yaml
json = hash.to_json

yaml_time = Benchmark.realtime do
  1000.times do
    YAML.load yaml
  end
end # => 5.85665

json_time = Benchmark.realtime do
  1000.times do
    JSON.load json
  end
end # => 0.012307

Thanks, I had forgotten that you can very easily define a new class for the same table to do neat tricks like this one.

When doing these steps in a Rails console, you need to use

faux_medium = Class.new ActiveRecord::Base do
  self.table_name = "media"
end

otherwise the first line results in an error, because it attempts to show something sensible for the new Class in the console and that attempt trigger an error, because no table name is set yet.

Thanks, very useful! 👍

Why use medium.send(:attribute, :payload) while not use medium.payload directly? My execution raises a error which said "undefined method `asstribute` for the class faux_medium".