Recently I ran into an issue trying to deploy to the Heroku Cedar stack for my (in progress) app, Mocknote. I developed the app locally with Sqlite3, using Sinatra and DataMapper.
Heroku complained about my Gemfile.lock missing the dm-postgres-adapter, but I was unable to install the gem locally. I resolved this conundrum by adding this to my Gemfile:
group :production do
gem 'dm-postgres-adapter'
end
I then ran this:
bundle install --without production
I was then able to successfully deploy to Heroku.
