Load database gems based on config/database.yml settings.

Gemfile

@@ -52,9 +52,33 @@ gem 'libv8'
 gem 'execjs'
 gem 'therubyracer'
 
-# e. g. for mysql you need to load mysql
-gem 'mysql2', '~> 0.3.20'
-gem 'pg'
+# Include database gems for the adapters found in the database
+# configuration file, thanks to redmine, taken from https://github.com/redmine/redmine/blob/master/Gemfile
+require 'erb'
+require 'yaml'
+database_file = File.join(File.dirname(__FILE__), 'config/database.yml')
+if File.exist?(database_file)
+  database_config = YAML.load(ERB.new(IO.read(database_file)).result)
+  adapters = database_config.values.map { |c| c['adapter'] }.compact.uniq
+  if adapters.any?
+    adapters.each do |adapter|
+      case adapter
+      when 'mysql2'
+        gem 'mysql2', '~> 0.3.20'
+      when /postgresql/
+        gem 'pg'
+      when /sqlite3/
+        gem 'sqlite3'
+      else
+        warn("Unknown database adapter `#{adapter}` found in config/database.yml, use Gemfile.local to load your own database gems")
+      end
+    end
+  else
+    warn('No adapter found in config/database.yml, please configure it first')
+  end
+else
+  warn('Please configure your config/database.yml first')
+end
 
 gem 'net-ldap'
 
@@ -97,3 +121,9 @@ group :development, :test do
 end
 
 gem 'puma'
+
+# load onw gem's
+local_gemfile = File.join(File.dirname(__FILE__), 'Gemfile.local')
+if File.exist?(local_gemfile)
+  eval_gemfile local_gemfile
+end

Gemfile.lock

@@ -154,7 +154,6 @@ GEM
     multi_json (1.11.2)
     multi_xml (0.5.5)
     multipart-post (2.0.0)
-    mysql2 (0.3.20)
     naught (1.1.0)
     nenv (0.2.0)
     net-ldap (0.13.0)
@@ -349,7 +348,6 @@ DEPENDENCIES
   libv8
   mail (~> 2.5.0)
   mime-types
-  mysql2 (~> 0.3.20)
   net-ldap
   omniauth
   omniauth-facebook