gem - why does rails generate scaffold fail? message is add pg to gemfile -

rails generate scaffold user name:string email:string
fails message gem::loaderror

the error message indicates gemfile not have gem pg does. says ensure version of pg @ minimum required activerecord. not sure minimum version of pg be.

so created new app start. database=postgresql option.

rails new app --database=postgresql

and answered yes new things created. set gemfile corectly. , rails generate scaffold success .