Rails 4 - Gem::LoadError: Specified 'mysql2' for database adapter, but the gem is not loaded

Question

In my gemfile I have:

gem 'mysql2'

My database.yml is as follows:

default: &default
  adapter: mysql2
  database: <%= ENV['db_name'] %>
  username: <%= ENV['db_user'] %>
  password: <%= ENV['db_pass'] %>
  host:     <%= ENV['db_host'] %>
  pool: 32
  socket:   <%= ENV['socket'] %>

development:
  <<: *default

production:
  <<: *default

I've run both bundle update and bundle install and my Gemfile.lock shows mysql2.

However when I run rake db:migrate I get this on both my computer and on the staging server:

myproject.com(master)$ rake db:migrate
WARNING: Use strings for Figaro configuration. 10000012508 was converted to "10000012508".
WARNING: Use strings for Figaro configuration. 860526407370038 was converted to "860526407370038".
rake aborted!
Gem::LoadError: Specified 'mysql2' for database adapter, but the gem is not loaded. Add `gem 'mysql2'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord).
.....

Just to make sure there wasn't a bad version of mysql2 or something, I did bundle clean --force and ran bundle install and bundle update again and when I run gem list I see mysql2 (0.4.0) and no other versions.

Any ideas would be most appreciated.

---

SOLUTION

It's currently an issue with Rails 4.1.x and 4.2.x, per this bug report, it will be fixed in the next release of rails 4.2.x (credit to dcorr in comments for the link).

In the mean time you can fix by doing downgraded to version 0.3.18 of mysql2 by adding this line to your gemfile:

gem 'mysql2', '~> 0.3.18'

Almandine

Try bundle update mysql2 – Foetation

I've tried that as well. Didn't work. From what I see the mysql2 (0.4.0) is the newest version ruby gems will take and it's already installed. – Almandine

Here was the solution: gem 'mysql2', '~> 0.3.18' in Gemfile. – Almandine

This isn't a bug with mysql2, it's a problem with the requirement in the ActiveRecord adapter: github.com/rails/rails/issues/21544. This is fixed in rails master: github.com/rails/rails/commit/… – Agribusiness

@Foetation Awsome maahn!! _/_ – Mckoy

If it's fixed in Rails master, can we pull from the Rails github repo URL to get that ver? – Hua

Your solution should be placed as an answer to your own question, not an edit. – Audriaaudrie

Answer 1

Just a further update - the solution in the question is correct.

The 4th comment is worth taking note of:

This isn't a bug with mysql2, it's a problem with the requirement in the ActiveRecord adapter: http://github.com/rails/rails/issues/21544. This is fixed in rails master: https://github.com/rails/rails/commit/5da5e3772c32593ecf2f27b8865e81dcbe3af692

I was able to tie Rails 4.2.4 to the 4-2-stable branch and get it working with the latest mysql2:

gem 'rails', '~> 4.2.4', git: "git://github.com/rails/rails.git", branch: '4-2-stable'
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw] #-> Rails 4.1+

#DB
gem 'mysql2'

Hua

If speed is a priority, it was a bit faster to bump mysql2 down to '0.3.20' instead of pinning rails '4.2.4' to branch: '4-2-stable'. – Isochroous

it's hard to believe that mysql gem has so many stingy buggy problems compares to postgreSQL T__T – Parquet

It's the Windows environment - it's the same with Imagemagick etc. You have to use external dependencies, and since Windows doesn't have a central repo for them, it gets tricky – Hua

What about Rails 5? – Hua

@RichardPeck I have this problem with Rails 5.0.3 – Talented

Works with Rails 5.1 – Hua

Answer 2

Just do:

gem 'mysql2', '~> 0.3.18' this gem works with rails version 4.x.x

if install gem 'mysql2', '~> 0.4.0' it produces gem load error and causes compatibility issues

Beauteous

Clean, simple and concise. Thanks! – Hocker

Worked for me @kaleem – Rafiq

Answer 3

This issue was addressed here: https://github.com/brianmario/mysql2/issues/950

For Rails 4.x please pin the gem to mysql2 '~> 0.4.0' to avoid the 0.5.x upgrade.

Gemfile:

gem 'rails', '4.2.8'
gem 'mysql2', '~> 0.4.0'

Then run bundle update rails mysql2

I am currently using mysql v 8.0.11

Defeasance

Answer 4

The answer to this particular question relative to when it was posted and the version of Rails being used is that the problem is caused from doing a bundle update and your mysql2 version updates to 0.4.x which has an incompatibility issue with latest Rails ActiveRecord.

Again, please note this is NOT the solution for people using older versions of Rails / ActiveRecord.

The quick solution is to simply specify the mysql2 version in your gemfile as follows:

gem 'mysql2', '0.3.20'

The long solution would be to wait for either an update to ActiveRecord or something in mysql2 to change.

Nicholas

Answer 5

If you are able to upgrade your rails version, then change your Gemfile to this and it will solve the problem without downgrading the mysql2 gem version:

gem 'rails', '4.2.6'

Turntable

Answer 6

As a complete beginner i got confused on how to do this so I just did a trial check and finally got my server working , here is how i got it working .

get into the file of working directory("work") and from there get into the file of the app you created("sample_app")which has mysql 2 installed go to gem file ("Gemfile")edit gem 'mysql2' to gem 'mysql2', '~> 0.3.18'

now go back to cmd and run command "bundle install".

so the directory to edit file taking consideration of above files in brackets should be . "c\work\sample_app\Gemfile"

hope i was of some help .

Bloodandthunder

Answer 7

This usually happens when you are missing some mysql packages on your machine. Do you get any errors from gem install mysql2? What OS are you working on?

If on debian or ubuntu try sudo apt-get install libmysqlclient-dev.

Also make sure that the gem is not placed inside a group statement in your Gemfile.

Grime

+1 for the assist. However I have libmysqlclient-dev already, and the gem is not inside a group statement. What's weird is that it works fine on my other projects, just not this one. Also this is not a new install of my OS I haven't changed anything in my environment for some time. And the same is true of the staging server, where I am seeing the same problems as well. – Almandine

Answer 8

Had same issue but adding source 'https://rubygems.org' to the top of gem file solved issue.

Steps:

add source 'https://rubygems.org' to your gem file. Comment out mysql2 gem and add gem 'mysql2', '~> 0.3.18' Run bundle install

Inherit

Answer 9

try this:

bundle update mysql2

this command will update your 'mysql2' gem to the latest version (should be 0.3.17 or higher) and start your rails server.

Pleuron

Answer 10

gem 'rails', '4.2.11.3'
gem 'mysql2', '~> 0.4.0'

Try this. This will remove the mysql2 load error.

Cultivator