Can't deploy Rails app to Heroku; complains about postgres when I'm not using any DB

Question

I've built my first rails app and I'm trying to deploy it to Heroku but the app just crashed every time I push. When I try to log into the rails console, this is what is see:

Running rails console attached to terminal... up, run.6183 /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/connection_specification.rb:177:in rescue in spec': Specified 'postgresql' for database adapter, but the gem is not loaded. Addgem 'pg'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord). (Gem::LoadError)

I'm not even using any database in my app. This is what my database.yml file looks like:

# SQLite version 3.x
#   gem install sqlite3
#
#   Ensure the SQLite 3 gem is defined in your Gemfile
#   gem 'sqlite3'
#

development:

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test:

production:

Can someone help me here?

Thanks!

Answer 1

The problem is that heroku will either rewrite database.yml or set environment variables that rails will pick up automatically.

You need to actually stop Activerecord loading:

To do this you replace require "rails/all" at the top of config/application.rb

With

require "action_controller/railtie"
require "action_mailer/railtie"
require "sprockets/railtie"
require "rails/test_unit/railtie"

You'll also need to remove anything in config/initializers or config/environments that references activerecord