Update Cardinals By delta for Postgresql.

Function

A gem to more safely update cardinal numbers like credits.

It will

• start a transaction
• make the change with a delta attr = attr + #{attributes[attr]}}
• call the given block with an indifferent hash of the latest values in the db.
• update the given attributes on the instance to the latest values.
• end transaction.

If any exceptions are thrown in the block, the change will automatically be reverted.

Sql will be like:

  update accounts set credits = credit + -20 where id = 6 returning credits

Usage:

gem 'update_cardinals_by', '~> 0.1.0'

update_cardinals_by!(credits: -20) do |res|
  fail 'not enough credits' if res[:credits] < 0
  CreateWantedItems.run(..)
  CreditMutation.create credits_new: res[:credits],
                        credits_old: credits,
                        credits_change: -20
end

Changelog

0.2.0 changed activerecord support to 5.2 and 6.0

0.1.0 changed activerecord support from 4.2 to 5.0 and 5.1

Developing

rake setup
rake db:setup
bundle exec appraisal install
bundle exec appraisal rspec