How to save a postgresql record into a backup table and restore it

pg_backup_with_hstore.rb

require 'pg'

# PG.connect(dbname: 'postgres').exec('create database josh_testing')
db = PG.connect(dbname: 'josh_testing').tap { |db| db.exec 'begin' }

# Make the db a little nicer to work with for our experiment
def db.exec(*)
  super.to_a
end


db.exec <<~SQL
  create extension hstore;

  create table backups (
    col_values hstore
  );

  -- test it against a table with some sophisticated types
  create type user_type    as enum ('admin', 'moderator', 'user');
  create type login_device as (name varchar, loggedin_at timestamp);
  create type hours        as range (subtype = time);
  create table users (
    id           serial primary key, -- an autoincrementing value
    name         varchar,            -- string
    type         user_type,          -- enum
    is_active    bool,               -- boolean
    preferences  hstore,             -- hstore (this will be nested)
    device       login_device,       -- composite type
    oncall_hours hours               -- a custom range
  );
  SQL

# create some users (but should work for an arbitrary table)
original = db.exec <<~SQL
  insert into users (name, type, is_active, preferences, device, oncall_hours)
  values ('Josh', 'admin', true, 'a=>b,c=>d', ('macbook', now()), hours('08:30 AM', '04:30 PM')),
         ('Sindy', 'moderator', false, '', null, null)
  returning *;
  SQL
  # => [{"id"=>"1",
  #      "name"=>"Josh",
  #      "type"=>"admin",
  #      "is_active"=>"t",
  #      "preferences"=>"\"a\"=>\"b\", \"c\"=>\"d\"",
  #      "device"=>"(macbook,\"2017-10-22 09:13:10.504474\")",
  #      "oncall_hours"=>"[08:30:00,16:30:00)"},
  #     {"id"=>"2",
  #      "name"=>"Sindy",
  #      "type"=>"moderator",
  #      "is_active"=>"f",
  #      "preferences"=>"",
  #      "device"=>nil,
  #      "oncall_hours"=>nil}]


# Back the users up
db.exec <<~SQL
  insert into backups (col_values)
  select hstore(users)
  from users
  returning *;
  SQL
  # => [{"col_values"=>
  #       "\"id\"=>\"1\", \"name\"=>\"Josh\", \"type\"=>\"admin\", \"device\"=>\"(macbook,\\\"2017-10-22 09:13:10.504474\\\")\", \"is_active\"=>\"t\", \"preferences\"=>\"\\\"a\\\"=>\\\"b\\\", \\\"c\\\"=>\\\"d\\\"\", \"oncall_hours\"=>\"[08:30:00,16:30:00)\""},
  #     {"col_values"=>
  #       "\"id\"=>\"2\", \"name\"=>\"Sindy\", \"type\"=>\"moderator\", \"device\"=>NULL, \"is_active\"=>\"f\", \"preferences\"=>\"\", \"oncall_hours\"=>NULL"}]


# Delete the users
db.exec <<~SQL
  delete from users;
  select * from users;
  SQL
  # => []

# Restore them from the backup
backed_up = db.exec <<~SQL
  insert into users
    select r.*
    from backups, populate_record(null::users, col_values) as r; 
  
  select * from users;
  SQL
  # => [{"id"=>"1",
  #      "name"=>"Josh",
  #      "type"=>"admin",
  #      "is_active"=>"t",
  #      "preferences"=>"\"a\"=>\"b\", \"c\"=>\"d\"",
  #      "device"=>"(macbook,\"2017-10-22 09:13:10.504474\")",
  #      "oncall_hours"=>"[08:30:00,16:30:00)"},
  #     {"id"=>"2",
  #      "name"=>"Sindy",
  #      "type"=>"moderator",
  #      "is_active"=>"f",
  #      "preferences"=>"",
  #      "device"=>nil,
  #      "oncall_hours"=>nil}]

# Do they match?
original == backed_up # => true