Install mysql2 on Mac OS - ruby

Question

I've install Ruby 2, Rails 4 and MySQL (with homebrew).
I tried to install the gem "mysql2" but i got this message :
gem install mysql2
Building native extensions. This could take a while...
ERROR: Error installing mysql2:
ERROR: Failed to build gem native extension.
/usr/local/rvm/rubies/ruby-2.0.0-p247/bin/ruby extconf.rb
checking for rb_thread_blocking_region()... yes
checking for rb_wait_for_single_fd()... yes
checking for mysql.h... no
checking for mysql/mysql.h... no
-----
mysql.h is missing. please check your installation of mysql and try again.
-----
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary libraries and/or headers. Check the mkmf.log file for more details. You may need configuration options.
Provided configuration options:
--with-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/usr/local/rvm/rubies/ruby-2.0.0-p247/bin/ruby
--with-mysql-config
--without-mysql-config
Gem files will remain installed in /usr/local/rvm/gems/ruby-2.0.0-p247/gems/mysql2-0.3.11 for inspection.
Results logged to /usr/local/rvm/gems/ruby-2.0.0-p247/gems/mysql2-0.3.11/ext/mysql2/gem_make.out
Can you help me ?

Answer 1

For some reason, install mysql via homebrew was broken. You have to manually edit the mysql_config.
The mysql_config file of homebrew stay in /usr/local/Cellar/mysql/5.6.12/bin,
Open it with sudo, around line 120, find these lines:
cflags="-I$pkgincludedir -Wall -Wno-null-conversion -Wno-unused-private-field -Os -g -fno-strict-aliasing -DDBUG_OFF -arch x86_64 " #note: end space!
cxxflags="-I$pkgincludedir -Wall -Wno-null-conversion -Wno-unused-private-field -Os -g -fno-strict-aliasing -DDBUG_OFF -arch x86_64 " #note: end space!
And remote -Wno-null-conversion -Wno-unused-private-filed in both line like this:
cflags="-I$pkgincludedir -Wall -Os -g -fno-strict-aliasing -DDBUG_OFF -arch x86_64 " #note: end space!
cxxflags="-I$pkgincludedir -Wall -Os -g -fno-strict-aliasing -DDBUG_OFF -arch x86_64 " #note: end space!
Save the file and execute brew install mysql again and it should work.
Check this blog post.

Answer 2

Check the compatibility of Rails and mysql version you are installing.
With me I was starting Rails 4.1.15 with Mysql 8.0 which didn't work and I came across similar errors.
Then i installed
brew install mysql56
Before this uninstall mysql if you have already installed one using -
brew uninstall mysql
brew cleanup
Now create a new rails project by specifying database to be used as mysql
rails new <PROJECT_NAME> -d mysql
This will create a new rails 4 project with compatible mysql
After this you can always configure the database.yml file for further details