Why is my 'pg' gem not being recognized? [duplicate] - ruby-on-rails

Question

This question already has answers here:
Heroku and Rails: Gem Load Error with Postgres, however it is Specified in GEMFILE
(3 answers)
Closed 5 years ago.
I know this question has come up before, but I have taken the advice from previous responses and I keep getting the same error. I don't know why my 'pg' gem is still not working:
source 'https://rubygems.org'
git_source(:github) do |repo_name|
repo_name = "#{repo_name}/#{repo_name}" unless repo_name.include?("/")
"https://github.com/#{repo_name}.git"
end
CODE:
# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '~> 5.1.2'
# Use sqlite3 as the database for Active Record
gem 'bcrypt', '~> 3.1.11'
gem 'bootstrap-sass', '3.3.7'
gem 'sprockets'
# gem 'sqlite3'
# Use Puma as the app server
gem 'puma', '~> 3.7'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# See https://github.com/rails/execjs#readme for more supported runtimes
# gem 'therubyracer', platforms: :ruby
# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.2'
# Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
gem 'turbolinks', '~> 5'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.5'
# Use Redis adapter to run Action Cable in production
# gem 'redis', '~> 3.0'
# Use ActiveModel has_secure_password
# gem 'bcrypt', '~> 3.1.7'
# Use Capistrano for deployment
# gem 'capistrano-rails', group: :development
group :development, :test do
# Call 'byebug' anywhere in the code to stop execution and get a debugger console
gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
# Adds support for Capybara system testing and selenium driver
gem 'capybara', '~> 2.13'
gem 'selenium-webdriver'
gem 'rails-controller-testing'
gem 'sqlite3'
end
group :development do
# Access an IRB console on exception pages or by using <%= console %> anywhere in the code.
gem 'web-console', '>= 3.3.0'
gem 'listen', '>= 3.0.5', '< 3.2'
# Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
gem 'spring'
gem 'spring-watcher-listen', '~> 2.0.0'
end
group :production do
gem 'rails_12factor'
gem 'pg', '0.20.0'
end
# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

Answer 1

It appears you're trying to use Postgres in your local environment, but your pg gem is in your production group. Bundler allows you to specify different environment groups for your gems, and you've specified that it should be used only in production. If you run bundle install it will still be installed, but it will not be required and used by the application. (You can skip installing the gems in your production group by running bundle install --without production)
If you are indeed trying to use Postgres locally, which you have not stated but I am inferring, you should move gem 'pg', '0.20.0' outside of the production group. You should also remove the sqlite3 gem, the default database adapter for new Rails projects, if you're not planning to use it.
# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '~> 5.1.2'
# Use sqlite3 as the database for Active Record
gem 'bcrypt', '~> 3.1.11'
gem 'bootstrap-sass', '3.3.7'
gem 'sprockets'
# gem 'sqlite3'
# Use Puma as the app server
gem 'puma', '~> 3.7'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# See https://github.com/rails/execjs#readme for more supported runtimes
# gem 'therubyracer', platforms: :ruby
# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.2'
# Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
gem 'turbolinks', '~> 5'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.5'
# Use Redis adapter to run Action Cable in production
# gem 'redis', '~> 3.0'
# Use ActiveModel has_secure_password
# gem 'bcrypt', '~> 3.1.7'
# PostgreSQL database
gem 'pg', '0.20.0'
# Use Capistrano for deployment
# gem 'capistrano-rails', group: :development
group :development, :test do
# Call 'byebug' anywhere in the code to stop execution and get a debugger console
gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
# Adds support for Capybara system testing and selenium driver
gem 'capybara', '~> 2.13'
gem 'selenium-webdriver'
gem 'rails-controller-testing'
end
group :development do
# Access an IRB console on exception pages or by using <%= console %> anywhere in the code.
gem 'web-console', '>= 3.3.0'
gem 'listen', '>= 3.0.5', '< 3.2'
# Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
gem 'spring'
gem 'spring-watcher-listen', '~> 2.0.0'
end
group :production do
gem 'rails_12factor'
end
# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

Answer 2

From this = gem 'pg', '0.20.0'
To this = gem 'pg', '~> 0.20.0'
This should be an easy syntax error.
Hope it helped.