Gem::LoadError: can't activate pg (~> 0.18), already activated pg-1.0.0 [duplicate]

Question

I've been doing the Rails tutorial found here and have been successful up to the point of having to migrate the Comments migration using $ rails db:migrate. Prior to this point, I've been able to generate the Article model and migrate the Articles create migration with no issues. In between these two migrations, nothing has changed in my Gemfile, so I'm not sure what it is Bundler is having an issue with.

Here are the errors, followed by the full command-line output, along with my Gemfile and schema.rb:

Gem::LoadError: can't activate pg (~> 0.18), already activated pg-1.0.0.  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). 

Full command-line output

xxx:gangelo: ~/dev/rails/test/blog (master*) ☠  rbenv exec rails db:migrate rails aborted! 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). /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/connection_adapters/connection_specification.rb:188:in `rescue in spec' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/connection_adapters/connection_specification.rb:185:in `spec' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:880:in `establish_connection' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/connection_handling.rb:58:in `establish_connection' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/railtie.rb:124:in `block (2 levels) in <class:Railtie>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/lazy_load_hooks.rb:69:in `instance_eval' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/lazy_load_hooks.rb:69:in `block in execute_hook' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/lazy_load_hooks.rb:60:in `with_execution_control' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/lazy_load_hooks.rb:65:in `execute_hook' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/lazy_load_hooks.rb:50:in `block in run_load_hooks' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/lazy_load_hooks.rb:49:in `each' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/lazy_load_hooks.rb:49:in `run_load_hooks' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/base.rb:326:in `<module:ActiveRecord>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/base.rb:25:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `block in require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:258:in `load_dependency' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/mysql_database_tasks.rb:6:in `<class:MySQLDatabaseTasks>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/mysql_database_tasks.rb:3:in `<module:Tasks>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/mysql_database_tasks.rb:2:in `<module:ActiveRecord>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/mysql_database_tasks.rb:1:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `block in require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:258:in `load_dependency' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/database_tasks.rb:74:in `<module:DatabaseTasks>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/database_tasks.rb:35:in `<module:Tasks>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/database_tasks.rb:2:in `<module:ActiveRecord>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/database_tasks.rb:1:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `block in require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:258:in `load_dependency' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/railtie.rb:34:in `block (3 levels) in <class:Railtie>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/railties-5.1.4/lib/rails/commands/rake/rake_command.rb:21:in `block in perform' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/railties-5.1.4/lib/rails/commands/rake/rake_command.rb:18:in `perform' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/railties-5.1.4/lib/rails/command.rb:46:in `invoke' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/railties-5.1.4/lib/rails/commands.rb:16:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/bin/rails:9:in `require' /Users/gangelo/dev/rails/test/blog/bin/rails:9:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/spring-2.0.2/lib/spring/client/rails.rb:28:in `load' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/spring-2.0.2/lib/spring/client/rails.rb:28:in `call' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/spring-2.0.2/lib/spring/client/command.rb:7:in `call' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/spring-2.0.2/lib/spring/client.rb:30:in `run' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/spring-2.0.2/bin/spring:49:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/spring-2.0.2/lib/spring/binstub.rb:31:in `load' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/spring-2.0.2/lib/spring/binstub.rb:31:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/bin/spring:15:in `<top (required)>' bin/rails:3:in `load' bin/rails:3:in `<main>'  Caused by: Gem::LoadError: can't activate pg (~> 0.18), already activated pg-1.0.0. Make sure all dependencies are added to Gemfile. /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/connection_adapters/postgresql_adapter.rb:2:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `block in require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:258:in `load_dependency' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/connection_adapters/connection_specification.rb:186:in `spec' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:880:in `establish_connection' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/connection_handling.rb:58:in `establish_connection' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/railtie.rb:124:in `block (2 levels) in <class:Railtie>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/lazy_load_hooks.rb:69:in `instance_eval' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/lazy_load_hooks.rb:69:in `block in execute_hook' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/lazy_load_hooks.rb:60:in `with_execution_control' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/lazy_load_hooks.rb:65:in `execute_hook' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/lazy_load_hooks.rb:50:in `block in run_load_hooks' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/lazy_load_hooks.rb:49:in `each' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/lazy_load_hooks.rb:49:in `run_load_hooks' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/base.rb:326:in `<module:ActiveRecord>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/base.rb:25:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `block in require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:258:in `load_dependency' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/mysql_database_tasks.rb:6:in `<class:MySQLDatabaseTasks>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/mysql_database_tasks.rb:3:in `<module:Tasks>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/mysql_database_tasks.rb:2:in `<module:ActiveRecord>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/mysql_database_tasks.rb:1:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `block in require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:258:in `load_dependency' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/database_tasks.rb:74:in `<module:DatabaseTasks>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/database_tasks.rb:35:in `<module:Tasks>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/database_tasks.rb:2:in `<module:ActiveRecord>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/tasks/database_tasks.rb:1:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `block in require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:258:in `load_dependency' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activesupport-5.1.4/lib/active_support/dependencies.rb:292:in `require' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/activerecord-5.1.4/lib/active_record/railtie.rb:34:in `block (3 levels) in <class:Railtie>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/railties-5.1.4/lib/rails/commands/rake/rake_command.rb:21:in `block in perform' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/railties-5.1.4/lib/rails/commands/rake/rake_command.rb:18:in `perform' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/railties-5.1.4/lib/rails/command.rb:46:in `invoke' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/railties-5.1.4/lib/rails/commands.rb:16:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/bin/rails:9:in `require' /Users/gangelo/dev/rails/test/blog/bin/rails:9:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/spring-2.0.2/lib/spring/client/rails.rb:28:in `load' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/spring-2.0.2/lib/spring/client/rails.rb:28:in `call' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/spring-2.0.2/lib/spring/client/command.rb:7:in `call' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/spring-2.0.2/lib/spring/client.rb:30:in `run' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/spring-2.0.2/bin/spring:49:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/spring-2.0.2/lib/spring/binstub.rb:31:in `load' /Users/gangelo/dev/rails/test/blog/vendor/bundle/gems/spring-2.0.2/lib/spring/binstub.rb:31:in `<top (required)>' /Users/gangelo/dev/rails/test/blog/bin/spring:15:in `<top (required)>' bin/rails:3:in `load' bin/rails:3:in `<main>' Tasks: TOP => db:migrate => db:load_config (See full trace by running task with --trace) 

Gemfile

source 'https://rubygems.org'  ruby '2.3.1'  git_source(:github) do |repo_name|   repo_name = "#{repo_name}/#{repo_name}" unless repo_name.include?("/")   "https://github.com/#{repo_name}.git" end   # Bundle edge Rails instead: gem 'rails', github: 'rails/rails' gem 'rails', '~> 5.1.4'  # Use sqlite3 as the database for Active Record # gem 'sqlite3'  # Use postgres as the database for Active Record gem 'pg'  # 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' end  # gma - start group :development, :test do   gem 'rspec-rails', '~> 3.5', '>= 3.5.2'   gem 'rspec-activemodel-mocks', '~> 1.0', '>= 1.0.3'   gem 'shoulda-matchers', '~> 3.1', '>= 3.1.1'   gem 'factory_bot_rails', '~> 4.8', '>= 4.8.2'   gem 'ffaker', '~> 2.2'   # gem 'timecop', '~> 0.8.1' end # gma - 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  # Windows does not include zoneinfo files, so bundle the tzinfo-data gem gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby] 

Schema.rb

ActiveRecord::Schema.define(version: 20180110153949) do   # These are extensions that must be enabled in order to support this database   enable_extension "plpgsql"    create_table "articles", force: :cascade do |t|     t.string "title"     t.text "text"     t.datetime "created_at", null: false     t.datetime "updated_at", null: false   end end 

Migration file

class CreateComments < ActiveRecord::Migration[5.1]   def change     create_table :comments do |t|       t.string :commenter       t.text :body       t.references :article, foreign_key: true        t.timestamps     end   end end 

Answer 1

looks like pg 1.0 is not compatible with rails 5.1.4 at the moment.

gem 'pg', '~> 0.18' 

0.18 worked for me.