When upgrading Rails, be sure to run
rake db:migrate even if you aren’t committing a migration. See if your
schema.rb changed. If it did, understand why, then commit the change along with the rest of the upgrade.
I was surprised by new
limit calls in my schema. Turns out that Rails 4.1.2 added information to the schema to ensure that MySQL
doubles are handled properly. Since we didn’t migrate for the upgrade job, they mysteriously appeared on the next migration.