RuntimeError with mysql2 and rails3 (bundler)

问题:

I get this error

`establish_connection': Please install the mysql2 adapter: `gem install activerecord-mysql2-adapter` (no such file to load -- active_record/connection_adapters/mysql2_adapter) (RuntimeError)
  from /opt/ruby-enterprise-1.8.7-2010.02/lib/ruby/gems/1.8/gems/activerecord-

Here is dump of whole error and my config and gemfile.

回答1:

I had the same error after upgrading from Ubuntu 11.10 to 12.04. This is how I fixed the problem:

gem uninstall mysql2
bundle

I think the key here is the 'native extensions' -- I suppose when I installed last, I was using a different version of mysql.

Installing mysql2 (0.3.11) with native extensions

回答2:

I was getting the same error while using rails 3.0.7 and mysql2 0.3.2. The solution, which I found here, is to use an older version of mysql2. Thus edit your gemfile to

gem 'mysql2', '< 0.3'

and run

bundle install 

回答3:

Also need to change adapter from mysql to mysql2 in database.yml as said here Install mysql2 gem on Snow Leopard for Rails 3 with rvm

From:

development: adapter: mysql

To:

development: adapter: mysql2

回答4:

Did you include the mysql2 gem in your gemfile instead of the old mysql gem, and ran bundle install afterwards?

回答5:

If you're using rvm, and possibly added mysql2 outside of rvm, try these steps: Confirm that your Gemfile says:

gem 'mysql2'

or for Rails2.x:

gem 'mysql2', '~> 0.2.11'

then:

$ cd RAILS_ROOT
$ gem uninstall mysql2

Select gem to uninstall:
 1. mysql2-0.2.11
 2. mysql2-0.3.6
 3. All versions
> 3 # select "All versions"
$ rvm gemset install mysql2
$ bundle install

Now rails should start properly.

回答6:

This also fixed the issue I had with:

Please install the mysql2 adapter: `gem install activerecord-mysql2-adapter` (no such file to load -- active_record/connection_adapters/mysql2_adapter)

You actually need to run: gem install mysql2 and add the gem to your config.

回答7:

just run "gem install mysql" also add the same in gemfile and run bundle. worked

回答8:

If anybody still facing problem of installing mysql2 gem with rails 3 on Windows, then refer to the detailed steps of installation on -

http://rorguide.blogspot.com/2011/03/installing-mysql2-gem-on-ruby-192-and.html

回答9:

I'm a beginner at ruby, rails, and linux. So if this solution did not work, I hold no responsibility :)

Step 1:

sudo gem uninstall mysql2

Step 2:

sudo gem install mysql -v 0.2.7

Start webrick, if the same problem still appears reinstall rails.

This solution works for me.

回答10:

Same issue for me too. Upgraded to Rails 3.1.rc4 then downgraded to 3.0.3. Worked for me.

回答11:

as of 0.3.0, and ActiveRecord 3.1 - the ActiveRecord adapter has been pulled out of this gem and into ActiveRecord itself. If you need to use mysql2 with Rails versions < 3.1 make sure and specify gem "mysql2", "~> 0.2.7" in your Gemfile

the missing file (no such file to load) can be found in the pre 0.3.0 versions of mysql2.

quoted from the documentation of mysql2