Using PostgreSQL's savepoints to recover from errors while inside a transaction

postgresql_savepoints_will_recover_from_errors_inside_transactions.rb

# these are Ruby 3's endless methods
require 'pg'
db = PG.connect
def db.exec_params(...) = super.map { |h| h.transform_keys &:intern }
def db.exec(...)        = super.map { |h| h.transform_keys &:intern }

# transactions methods
def db.begin()           = exec('begin')
def db.save(name)        = exec("savepoint #{name}")
def db.rollback_to(name) = exec("rollback to #{name}")

def db.select() = exec("select * from omgs")
def db.insert(*vals) = exec_params(<<~SQL, vals)
  insert into omgs (val)
  values #{vals.map.with_index(1) { |_, i| "($#{i})" }.join(", ")}
  returning *
SQL

# A transaction with a table and 3 rows
db.begin
db.exec 'create table omgs(val integer)'
db.insert 11, 22
db.save 'has_1122'

# We can rollback the inserted data while still leaving the transaction open
db.insert 33, 44
db.select # => [{:val=>"11"}, {:val=>"22"}, {:val=>"33"}, {:val=>"44"}]
db.rollback_to 'has_1122'
db.select # => [{:val=>"11"}, {:val=>"22"}]

# Errors will prevent us from running new commands
# becuase "current transaction is aborted"
db.insert 55, 66
db.select                # => [{:val=>"11"}, {:val=>"22"}, {:val=>"55"}, {:val=>"66"}]
db.exec 'omg!' rescue $! # => #<PG::SyntaxError: ERROR:  syntax error at or near "omg"\nLINE 1: omg!\n        ^\n>
db.select      rescue $! # => #<PG::InFailedSqlTransaction: ERROR:  current transaction is aborted, commands ignored until end of transaction block\n>

# But we can rollback to that last savepoint and then try again
db.rollback_to 'has_1122'
db.select # => [{:val=>"11"}, {:val=>"22"}]