Publishing Rails 5 apps to heroku

When attempting to migrate the database, I was getting errors with the following two messages

Gem::LoadError: Specified 'postgresql' for database adapter, but the gem is not loaded. Add `gem 'pg'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord).

Gem::LoadError: can't activate pg (~> 0.18), already activated pg-1.0.0. Make sure all dependencies are added to Gemfile.

The second one turned out to be the main issue.

A solution was found in a rails issue 31669, briefly

Thank you for the issue. Rails still don't support pg 1.0.

My solution was to change the Gemfile reference to

group :production do

gem 'pg', '~> 0.18'

gem 'rails_12factor'

end

And the migration succeeded. Now to apply the issue to the other app I was looking at yesterday...