activeRecord::ConnectionNot Established No connection pool with id primary found: mysql2

im very new to ruby on rails. and learning ruby on rails by a tutorials: Lynda.com - Ruby on Rails 4 Essential Training with kavin skoglund. all was going fine, unttil, i run my application first time which means "http://localhost:3000" i get this error: activeRecord::ConnectionNotEstablished No connection pool with id primary found.

im using Rails 5.0.0 ruby 2.3.1 mysql2

it is completely configure in Gemfile and config\database.yml.

if I go for splite3 to solve this problem, then i can not follow this tutorial. can anyone help me to solve this issue while i have mysql2 as my database. Adeel Ahmed. http://adeelahmed.net