红宝石在Rails上的MySQL错误新的应用程序数据库未知

Question

i have installed ruby on trails with mysql.

i installed mysql using command

 sudo apt-get install mysql-server

A promt appears to ask for password, I set it to 1234 and again a promt to confirm the password appears.

I also installed the mysql2 gem using

gem install mysql2

and created a new rails app using

rails new app -d mysql

The new app was created successfully but when I start the server with rails server and open http://localhost:3000 an error occurred:

unknown database

The whole stacktrace is given below

mysql2 (0.3.14) lib/mysql2/client.rb:67:in `connect'
mysql2 (0.3.14) lib/mysql2/client.rb:67:in `initialize'
activerecord (4.0.0) lib/active_record/connection_adapters/mysql2_adapter.rb:18:in `new'
activerecord (4.0.0) lib/active_record/connection_adapters/mysql2_adapter.rb:18:in `mysql2_connection'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:440:in `new_connection'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:450:in `checkout_new_connection'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:421:in `acquire_connection'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:356:in `block in checkout'
/home/sana/.rvm/rubies/ruby-2.0.0-p353/lib/ruby/2.0.0/monitor.rb:211:in `mon_synchronize'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:355:in `checkout'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:265:in `block in connection'
/home/sana/.rvm/rubies/ruby-2.0.0-p353/lib/ruby/2.0.0/monitor.rb:211:in `mon_synchronize'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:264:in `connection'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:546:in `retrieve_connection'
activerecord (4.0.0) lib/active_record/connection_handling.rb:79:in `retrieve_connection'
activerecord (4.0.0) lib/active_record/connection_handling.rb:53:in `connection'
activerecord (4.0.0) lib/active_record/query_cache.rb:51:in `restore_query_cache_settings'
activerecord (4.0.0) lib/active_record/query_cache.rb:43:in `rescue in call'
activerecord (4.0.0) lib/active_record/query_cache.rb:32:in `call'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:626:in `call'
activerecord (4.0.0) lib/active_record/migration.rb:369:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.0.0) lib/active_support/callbacks.rb:373:in `_run__695031866633904995__call__callbacks'
activesupport (4.0.0) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/reloader.rb:64:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.0.0) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.0.0) lib/rails/rack/logger.rb:21:in `block in call'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `block in tagged'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:25:in `tagged'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `tagged'
railties (4.0.0) lib/rails/rack/logger.rb:21:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.5.2) lib/rack/methodoverride.rb:21:in `call'
rack (1.5.2) lib/rack/runtime.rb:17:in `call'
activesupport (4.0.0) lib/active_support/cache/strategy/local_cache.rb:83:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/static.rb:64:in `call'
railties (4.0.0) lib/rails/engine.rb:511:in `call'
railties (4.0.0) lib/rails/application.rb:97:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
rack (1.5.2) lib/rack/content_length.rb:14:in `call'
rack (1.5.2) lib/rack/handler/webrick.rb:60:in `service'
/home/sana/.rvm/rubies/ruby-2.0.0-p353/lib/ruby/2.0.0/webrick/httpserver.rb:138:in `service'
/home/sana/.rvm/rubies/ruby-2.0.0-p353/lib/ruby/2.0.0/webrick/httpserver.rb:94:in `run'
/home/sana/.rvm/rubies/ruby-2.0.0-p353/lib/ruby/2.0.0/webrick/server.rb:295:in `block in start_thread'

where is the error??

config/database.yml

development:
  adapter: mysql2
  encoding: utf8
  database: mysqltestapp_development
  pool: 5
  username: root
  password: 1234
  host: 127.0.0.1
  socket: /var/run/mysqld/mysqld.sock

Answer 1

Assuming the error message is something similar to

error occured unknown database

It means the database doesn't exist. Make sure you created it in MySQL (Rails does not create it automatically).

mysql -e 'create database mysqltestapp_development;'

If the app is not new, you should also load the schema.

rake db:schema:load