Gem::LoadError: can't activate mysql2 (< 0.5, >= 0.3.18), already activated mysql2-0.5.0

问题

I did bundle install and the mysql2 gem was updated from 0.4.10 to 0.5.0.

After this anything involving ActiveRecord blows up with the error in the title.

回答1:

ActiveRecord only works with specific versions of mysql2.

In your Gemfile add:

gem 'mysql2', '< 0.5'

and bundle install.

I would also recommend adding a comment pointing to this URL so you know why the gem is pinned.

来源：https://stackoverflow.com/questions/49407254/gemloaderror-cant-activate-mysql2-0-5-0-3-18-already-activated-mysq