Rails mysql2, undefined method 'accept' for nil:NilClass on rake db:migrate

Question

So I'm working in a Rails application that has the following in the Gemfile:

gem 'mysql2', '< 0.4'

I proceeded with the following:

• bundle install
• rake db:create

From here I get

An error occurred while installing mysql2 (0.3.21), and Bundler cannot continue.

So I update it to

gem 'mysql2', '~> 0.4.10'

Run bundle install and rake db:create.

So I end up with

LoadError: Please install the mysql2 adapter: gem install activerecord-mysql2-adapter (can't activate mysql2 (~> 0.3.10), already activated mysql2-0.4.10. Make sure all dependencies are added to Gemfile.)

Gem::LoadError: can't activate mysql2 (~> 0.3.10), already activated mysql2-0.4.10. Make sure all dependencies are added to Gemfile.

From here if I try rails console I end up with:

block (2 levels) in replace_gem': Please install the mysql2 adapter: gem install activerecord-mysql2-adapter` (can't activate mysql2 (~> 0.3.10), already activated mysql2-0.4.10. Make sure all dependencies are added to Gemfile.) (LoadError)

So I update my gemfile to have:

gem 'mysql2', '~> 0.4.10' gem 'activerecord-mysql2-adapter'

Rails console works but rake db:migrate results in

rake aborted! NoMethodError: undefined method `accept' for nil:NilClass

And everything I've found for solutions was to remove activerecord-mysql2-adapter...and that doesn't work.

For reference I'm using: ruby 2.3.5, rails 3.2.22.5

Answer 1

If you're using an obsolete version of Rails (and 3.2 is extremely out of date) you'll need to use a compatible version of mysql2. If that's 0.3.21 then:

gem 'mysql2', '~> 0.3.21'

Nothing else will work.