gem mysql2 on Raspberry Pi Ruby 2.2.4 - ruby

Question

i tried for a few weeks to install mysql2 for ruby so i can use it with dashing. But the only thing i get is:
gem install mysql2 --platform=ruby -- '--with-mysql-dir="/usr/include/mysql"'
Building native extensions with: '--with-mysql-dir="/usr/include/mysql"'
This could take a while...
ERROR: Error installing mysql2:
ERROR: Failed to build gem native extension.
/usr/local/rvm/rubies/ruby-2.2.4/bin/ruby -r ./siteconf20160203-7890-abpifj.rb extconf.rb --with-mysql-dir="/usr/include/mysql"
checking for ruby/thread.h... yes
checking for rb_thread_call_without_gvl() in ruby/thread.h... yes
checking for rb_thread_blocking_region()... no
checking for rb_wait_for_single_fd()... yes
checking for rb_hash_dup()... yes
checking for rb_intern3()... yes
-----
Cannot find include dir(s) /usr/include/mysql/include
-----
*** 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
--without-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-2.2.4/bin/$(RUBY_BASE_NAME)
--with-mysql-dir
--with-mysql-include
--without-mysql-include=${mysql-dir}/include
--with-mysql-lib
--without-mysql-lib=${mysql-dir}/lib
extconf failed, exit code 1
Gem files will remain installed in /usr/local/rvm/gems/ruby-2.2.4/gems/mysql2-0.4.2 for inspection.
Results logged to /usr/local/rvm/gems/ruby-2.2.4/extensions/armv7l-linux/2.2.0/mysql2-0.4.2/gem_make.out
it is a Raspberry Pi 2 with Ruby 2.2.4 via RVM installed.
libmysqlclient-dev is installed.
mkmf.log tells me:
have_func: checking for rb_thread_blocking_region()... -------------------- no
"gcc -o conftest -I/usr/local/rvm/rubies/ruby-2.2.4/include/ruby-2.2.0/armv7l-linux-eabihf -I/usr/local/rvm/rubies/ruby-2.2.4/include/ruby-2.2.0/ruby/backward -I/usr/local/rvm/rubies/ruby-2.2.4/include/ruby-2.2.0 -I. -D_FILE_OFFSET_BITS=64$
conftest.c: In function ‘t’:
conftest.c:13:57: error: ‘rb_thread_blocking_region’ undeclared (first use in this function)
conftest.c:13:57: note: each undeclared identifier is reported only once for each function it appears in
conftest.c:13:32: warning: variable ‘p’ set but not used [-Wunused-but-set-variable]

Answer 1

It looks like there is a bug in the mysql2 gem you're trying to install.
Try install the previous stable version, 0.3.X
gem install mysql2 --platform=ruby -v '~> 0.3.0'
If that doesn't work, try update your Ruby version.
sudo apt-get install ruby2.2
Or, if you can, upgrade
sudo apt-get install ruby2.3

Answer 2

Install the raspbian specific package, before trying to get the gem this worked for me.
apt-get install ruby-mysql2
ruby new projectname -dmysql

Answer 3

I finally got around this error with the following:
apt-get install libmysql++-dev

Answer 4

you should
apt-get install libmariadbclient-dev