Ruby on Rails cannot connect to mysql database

Question

I have mysql installed via homebrew. Created the database prestamoApp_development I started the server (mysql.server start) and then created a new empty project (rails new prestamoApp -d mysql). Finally configured the user and password in the database.yml file like this:

default: &default
  adapter: mysql2
  encoding: utf8
  pool: 5
  username: root
  password: pqdsimple
  socket: /tmp/mysql.sock

development:
  <<: *default
  database: prestamoApp_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:
  <<: *default
  database: prestamoApp_test

# As with config/secrets.yml, you never want to store sensitive information,
# like your database password, in your source code. If your source code is
# ever seen by anyone, they now have access to your database.
#
# Instead, provide the password as a unix environment variable when you boot
# the app. Read http://guides.rubyonrails.org/configuring.html#configuring-a-database
# for a full rundown on how to provide these environment variables in a
# production deployment.
#
# On Heroku and other platform providers, you may have a full connection URL
# available as an environment variable. For example:
#
#   DATABASE_URL="mysql2://myuser:mypass@localhost/somedatabase"
#
# You can use this database configuration with:
#
#   production:
#     url: <%= ENV['DATABASE_URL'] %>
#
production:
  <<: *default
  database: prestamoApp_production
  username: prestamoApp
  password: <%= ENV['PRESTAMOAPP_DATABASE_PASSWORD'] %>

this is the gem file:

source 'https://rubygems.org'


# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.2.4'
# Use mysql as the database for Active Record
gem 'mysql2'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.1.0'
# See https://github.com/rails/execjs#readme for more supported runtimes
# gem 'therubyracer', platforms: :ruby

# Use jquery as the JavaScript library
gem 'jquery-rails'
# Turbolinks makes following links in your web application faster. Read more: https://github.com/rails/turbolinks
gem 'turbolinks'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.0'
# bundle exec rake doc:rails generates the API under doc/api.
gem 'sdoc', '~> 0.4.0', group: :doc

# Use ActiveModel has_secure_password
# gem 'bcrypt', '~> 3.1.7'

# Use Unicorn as the app server
# gem 'unicorn'

# 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'
end

group :development do
  # Access an IRB console on exception pages or by using <%= console %> in views
  gem 'web-console', '~> 2.0'

  # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
  gem 'spring'
end

and just in case the gem file.lock:

GEM
  remote: https://rubygems.org/
  specs:
    actionmailer (4.2.4)
      actionpack (= 4.2.4)
      actionview (= 4.2.4)
      activejob (= 4.2.4)
      mail (~> 2.5, >= 2.5.4)
      rails-dom-testing (~> 1.0, >= 1.0.5)
    actionpack (4.2.4)
      actionview (= 4.2.4)
      activesupport (= 4.2.4)
      rack (~> 1.6)
      rack-test (~> 0.6.2)
      rails-dom-testing (~> 1.0, >= 1.0.5)
      rails-html-sanitizer (~> 1.0, >= 1.0.2)
    actionview (4.2.4)
      activesupport (= 4.2.4)
      builder (~> 3.1)
      erubis (~> 2.7.0)
      rails-dom-testing (~> 1.0, >= 1.0.5)
      rails-html-sanitizer (~> 1.0, >= 1.0.2)
    activejob (4.2.4)
      activesupport (= 4.2.4)
      globalid (>= 0.3.0)
    activemodel (4.2.4)
      activesupport (= 4.2.4)
      builder (~> 3.1)
    activerecord (4.2.4)
      activemodel (= 4.2.4)
      activesupport (= 4.2.4)
      arel (~> 6.0)
    activesupport (4.2.4)
      i18n (~> 0.7)
      json (~> 1.7, >= 1.7.7)
      minitest (~> 5.1)
      thread_safe (~> 0.3, >= 0.3.4)
      tzinfo (~> 1.1)
    arel (6.0.3)
    binding_of_caller (0.7.2)
      debug_inspector (>= 0.0.1)
    builder (3.2.2)
    byebug (6.0.2)
    coffee-rails (4.1.0)
      coffee-script (>= 2.2.0)
      railties (>= 4.0.0, < 5.0)
    coffee-script (2.4.1)
      coffee-script-source
      execjs
    coffee-script-source (1.9.1.1)
    debug_inspector (0.0.2)
    erubis (2.7.0)
    execjs (2.6.0)
    globalid (0.3.6)
      activesupport (>= 4.1.0)
    i18n (0.7.0)
    jbuilder (2.3.1)
      activesupport (>= 3.0.0, < 5)
      multi_json (~> 1.2)
    jquery-rails (4.0.5)
      rails-dom-testing (~> 1.0)
      railties (>= 4.2.0)
      thor (>= 0.14, < 2.0)
    json (1.8.3)
    loofah (2.0.3)
      nokogiri (>= 1.5.9)
    mail (2.6.3)
      mime-types (>= 1.16, < 3)
    mime-types (2.6.1)
    mini_portile (0.6.2)
    minitest (5.8.0)
    multi_json (1.11.2)
    mysql2 (0.4.0)
    nokogiri (1.6.6.2)
      mini_portile (~> 0.6.0)
    rack (1.6.4)
    rack-test (0.6.3)
      rack (>= 1.0)
    rails (4.2.4)
      actionmailer (= 4.2.4)
      actionpack (= 4.2.4)
      actionview (= 4.2.4)
      activejob (= 4.2.4)
      activemodel (= 4.2.4)
      activerecord (= 4.2.4)
      activesupport (= 4.2.4)
      bundler (>= 1.3.0, < 2.0)
      railties (= 4.2.4)
      sprockets-rails
    rails-deprecated_sanitizer (1.0.3)
      activesupport (>= 4.2.0.alpha)
    rails-dom-testing (1.0.7)
      activesupport (>= 4.2.0.beta, < 5.0)
      nokogiri (~> 1.6.0)
      rails-deprecated_sanitizer (>= 1.0.1)
    rails-html-sanitizer (1.0.2)
      loofah (~> 2.0)
    railties (4.2.4)
      actionpack (= 4.2.4)
      activesupport (= 4.2.4)
      rake (>= 0.8.7)
      thor (>= 0.18.1, < 2.0)
    rake (10.4.2)
    rdoc (4.2.0)
    sass (3.4.18)
    sass-rails (5.0.4)
      railties (>= 4.0.0, < 5.0)
      sass (~> 3.1)
      sprockets (>= 2.8, < 4.0)
      sprockets-rails (>= 2.0, < 4.0)
      tilt (>= 1.1, < 3)
    sdoc (0.4.1)
      json (~> 1.7, >= 1.7.7)
      rdoc (~> 4.0)
    spring (1.3.6)
    sprockets (3.3.4)
      rack (~> 1.0)
    sprockets-rails (2.3.3)
      actionpack (>= 3.0)
      activesupport (>= 3.0)
      sprockets (>= 2.8, < 4.0)
    thor (0.19.1)
    thread_safe (0.3.5)
    tilt (2.0.1)
    turbolinks (2.5.3)
      coffee-rails
    tzinfo (1.2.2)
      thread_safe (~> 0.1)
    uglifier (2.7.2)
      execjs (>= 0.3.0)
      json (>= 1.8.0)
    web-console (2.2.1)
      activemodel (>= 4.0)
      binding_of_caller (>= 0.7.2)
      railties (>= 4.0)
      sprockets-rails (>= 2.0, < 4.0)

PLATFORMS
  ruby

DEPENDENCIES
  byebug
  coffee-rails (~> 4.1.0)
  jbuilder (~> 2.0)
  jquery-rails
  mysql2
  rails (= 4.2.4)
  sass-rails (~> 5.0)
  sdoc (~> 0.4.0)
  spring
  turbolinks
  uglifier (>= 1.3.0)
  web-console (~> 2.0)

BUNDLED WITH
   1.10.6

When I try to do this:

rake db:schema:dump

I get this error:

rake aborted!
Gem::LoadError: Specified 'mysql2' for database adapter, but the gem is not loaded. Add `gem 'mysql2'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord).
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/connection_adapters/connection_specification.rb:177:in `rescue in spec'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/connection_adapters/connection_specification.rb:174:in `spec'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/connection_handling.rb:50:in `establish_connection'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/railtie.rb:120:in `block (2 levels) in <class:Railtie>'
/usr/local/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/lazy_load_hooks.rb:38:in `instance_eval'
/usr/local/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/lazy_load_hooks.rb:38:in `execute_hook'
/usr/local/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/lazy_load_hooks.rb:45:in `block in run_load_hooks'
/usr/local/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/lazy_load_hooks.rb:44:in `each'
/usr/local/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/lazy_load_hooks.rb:44:in `run_load_hooks'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/base.rb:315:in `<module:ActiveRecord>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/base.rb:26:in `<top (required)>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/mysql_database_tasks.rb:8:in `<class:MySQLDatabaseTasks>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/mysql_database_tasks.rb:3:in `<module:Tasks>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/mysql_database_tasks.rb:2:in `<module:ActiveRecord>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/mysql_database_tasks.rb:1:in `<top (required)>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:50:in `<module:DatabaseTasks>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:37:in `<module:Tasks>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:4:in `<module:ActiveRecord>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:3:in `<top (required)>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/railtie.rb:41:in `block (3 levels) in <class:Railtie>'
Gem::LoadError: can't activate mysql2 (~> 0.3.13), already activated mysql2-0.4.0. Make sure all dependencies are added to Gemfile.
/usr/local/lib/ruby/gems/2.2.0/gems/bundler-1.10.6/lib/bundler/rubygems_integration.rb:302:in `block in replace_gem'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/connection_adapters/mysql2_adapter.rb:3:in `<top (required)>'
/usr/local/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:274:in `require'
/usr/local/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:274:in `block in require'
/usr/local/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:240:in `load_dependency'
/usr/local/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:274:in `require'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/connection_adapters/connection_specification.rb:175:in `spec'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/connection_handling.rb:50:in `establish_connection'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/railtie.rb:120:in `block (2 levels) in <class:Railtie>'
/usr/local/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/lazy_load_hooks.rb:38:in `instance_eval'
/usr/local/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/lazy_load_hooks.rb:38:in `execute_hook'
/usr/local/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/lazy_load_hooks.rb:45:in `block in run_load_hooks'
/usr/local/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/lazy_load_hooks.rb:44:in `each'
/usr/local/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/lazy_load_hooks.rb:44:in `run_load_hooks'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/base.rb:315:in `<module:ActiveRecord>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/base.rb:26:in `<top (required)>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/mysql_database_tasks.rb:8:in `<class:MySQLDatabaseTasks>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/mysql_database_tasks.rb:3:in `<module:Tasks>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/mysql_database_tasks.rb:2:in `<module:ActiveRecord>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/mysql_database_tasks.rb:1:in `<top (required)>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:50:in `<module:DatabaseTasks>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:37:in `<module:Tasks>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:4:in `<module:ActiveRecord>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:3:in `<top (required)>'
/usr/local/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/railtie.rb:41:in `block (3 levels) in <class:Railtie>'
Tasks: TOP => db:schema:dump => db:load_config
(See full trace by running task with --trace)

Can somebody please tell me what is wrong? What do I need to do in order to solve this problem, I've done nothing but creating an empty project.

Answer 1

Just downgrade mysql gem gem 'mysql2', '~> 0.3.20'

It's a bug

Answer 2

For new coders (like me) gem 'mysql2', '~> 0.3.20' is NOT a command! You will get the error "Unknown command mysql2" if you try.

vi/Edit the Gemfile and append replace

gem 'mysql2'

with

gem 'mysql2', '~> 0.3.20'

save

then type the command:

bundle install

Then retry your rake db:________ command.