Examples to explore possible race conditions when caching custom computed values in Rails

In Rails, sometimes you will need to save counts or custom computed values, where the default counter cache will not be enough.Maybe you want to…Update a counter cache when a value change and not only when the association is created or deleted.Have a counter cache for complex “has many through” associations.Keep a count for a scope of the association, like just the “positive reactions”, or the “completed orders”.Cache a sum or another calculation like the “account balance”.