Just Another ActiveRecord::ConnectionNotEstablished Question

I am trying to follow RESTful Rails Development from O’Reilly by Silvia

I have created an app (wikicat), database (MySQL), models (category and
link), controllers (CategoryController show) and routes. I have followed
everything that the book said (taking in to consideration the published
errata) and I am going round and round in circles trying to fix an
ActiveRecord::ConnectionNotEstablished error.

I am running on Linux Mint 17.2 with:

Rails version 4.1.4
mysql version 14.14 Distribution 5.5.46

I have started mysql server. My Gemfile has been bundled and is shown

source ‘https://rubygems.org

Bundle edge Rails instead: gem ‘rails’, github: ‘rails/rails’

gem ‘rails’, ‘4.1.4’
gem ‘rails-api’

Use mysql as the database for Active Record

gem ‘mysql2’, ‘~> 0.3.18’

#Serialiser for JSON
gem ‘active_model_serializers’
group :doc do
#bundle exec rake doc:rails generates the API under doc/api
gem ‘sdoc’, ‘~>0.4.0’
group :development do
#Spring speeds up development by keeping your application
#running in the background. Read more:
gem ‘spring’

There isn’t an application trace, but there is a framework trace which I
have pasted below:

activerecord (4.1.4)
retrieve_connection' activerecord (4.1.4) lib/active_record/connection_handling.rb:113:inretrieve_connection’
activerecord (4.1.4) lib/active_record/connection_handling.rb:87:in
connection' activerecord (4.1.4) lib/active_record/migration.rb:388:incheck_pending!’
activerecord (4.1.4) lib/active_record/migration.rb:377:in call' actionpack (4.1.4) lib/action_dispatch/middleware/callbacks.rb:29:inblock in call’
activesupport (4.1.4) lib/active_support/callbacks.rb:82:in
run_callbacks' actionpack (4.1.4) lib/action_dispatch/middleware/callbacks.rb:27:incall’
actionpack (4.1.4) lib/action_dispatch/middleware/reloader.rb:73:in
call' actionpack (4.1.4) lib/action_dispatch/middleware/remote_ip.rb:76:incall’
actionpack (4.1.4)
lib/action_dispatch/middleware/debug_exceptions.rb:17:in call' actionpack (4.1.4) lib/action_dispatch/middleware/show_exceptions.rb:30:incall’
railties (4.1.4) lib/rails/rack/logger.rb:38:in call_app' railties (4.1.4) lib/rails/rack/logger.rb:20:inblock in call’
activesupport (4.1.4) lib/active_support/tagged_logging.rb:68:in block in tagged' activesupport (4.1.4) lib/active_support/tagged_logging.rb:26:intagged’
activesupport (4.1.4) lib/active_support/tagged_logging.rb:68:in
tagged' railties (4.1.4) lib/rails/rack/logger.rb:20:incall’
actionpack (4.1.4) lib/action_dispatch/middleware/request_id.rb:21:in
call' rack (1.5.5) lib/rack/runtime.rb:17:incall’
activesupport (4.1.4)
lib/active_support/cache/strategy/local_cache_middleware.rb:26:in call' rack (1.5.5) lib/rack/lock.rb:17:incall’
actionpack (4.1.4) lib/action_dispatch/middleware/static.rb:64:in call' railties (4.1.4) lib/rails/engine.rb:514:incall’
railties (4.1.4) lib/rails/application.rb:144:in call' rack (1.5.5) lib/rack/lock.rb:17:incall’
rack (1.5.5) lib/rack/content_length.rb:14:in call' rack (1.5.5) lib/rack/handler/webrick.rb:60:inservice’
/usr/lib/ruby/1.9.1/webrick/httpserver.rb:138:in service' /usr/lib/ruby/1.9.1/webrick/httpserver.rb:94:inrun’
/usr/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread’

Is there anything in there telling me why I can’t get a connection?
Thank you for your patience with my newbie query.

  1. Did you install mysql properly?
    a) Try to connect to mysql server from a command line, and run some
    simple queries against your database.
    b) Create a simple (pure) Ruby application and try to connect to your
    database from this application.

If it works fine, then your problem is Rails based.

  1. Have a look at database.yml file.