Initial untested version

Gemfile

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+source 'https://rubygems.org'
+
+# Specify your gem's dependencies in hiera-mysql-backend.gemspec
+gemspec

Gemfile.lock

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+PATH
+  remote: .
+  specs:
+    hiera-mysql-backend (0.0.1)
+      mysql2
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    mysql2 (0.3.13)
+    rake (10.1.0)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  hiera-mysql-backend!
+  rake

Rakefile

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+require "bundler/gem_tasks"

hiera-mysql-backend.gemspec

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+# -*- encoding: utf-8 -*-
+
+Gem::Specification.new do |gem|
+  gem.name          = "hiera-mysql-backend"
+  gem.version       = "0.0.1"
+  gem.authors       = ["Telmo"]
+  gem.email         = ["[email protected]"]
+  gem.description   = %q{Alternative MySQL backend for hiera}
+  gem.summary       = %q{Alternative MySQL backend for hiera}
+  gem.homepage      = "https://github.com/Telmo/hiera-mysql-backend"
+
+  gem.files         = `git ls-files`.split($/)
+  gem.executables   = gem.files.grep(%r{^bin/}).map{ |f| File.basename(f) }
+  gem.test_files    = gem.files.grep(%r{^(test|spec|features)/})
+  gem.require_paths = ["lib"]
+  gem.add_dependency('mysql2')
+  gem.add_development_dependency('rake')
+end

lib/hiera/backend/mysql_backend.rb

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+class Hiera
+  module Backend
+    class Mysql_backend
+
+      def initialize(cache=nil)
+        begin
+          require 'mysql2'
+        rescue LoadError
+          require 'rubygems'
+          require 'mysql2'
+        end
+
+        @cache = cache || Filecache.new
+
+        Hiera.debug("Hiera MySQL initialized")
+      end
+
+      def lookup(key, scope, order_override, resolution_type)
+        # default answer just to make it easier on ourselves
+        answer = nil
+
+        Hiera.debug("looking up %{key} in MySQL Backend")
+        Hiera.debug("resolution type is #{resolution_type}")
+
+        Backend.datasources(scope, order_override) do |source|
+          Hiera.debug("Looking for data source #{source}")
+          sqlfile = Backend.datafile(:sql, scope, source, "sql") || next
+
+          next unless File.exist?(sqlfile)
+          data = @cache.read(sqlfile, Hash, {}) do |data|
+            YAML.load(data)
+          end
+
+          next if data.empty?
+          next unless data.include?(key)
+
+          Hiera.debug("Found #{key} in #{source}")
+
+          new_answer = Backend.parse_answer(data[key], scope)
+          results = query(new_answer)
+          return results
+        end
+
+
+        def query(query)
+          Hiera.debug("Executing SQL Query: #{sql}")
+
+          data=[]
+          mysql_host = Config[:mysql][:host]
+          mysql_user = Config[:mysql][:user]
+          mysql_pass = Config[:mysql][:pass]
+          mysql_database = Config[:mysql][:database]
+          client = Mysql2::Client.new(:host => mysql_host, 
+                                      :username => mysql_username, 
+                                      :password => mysql_pass, 
+                                      :database => mysql_database,
+                                      :reconnect => true)
+          begin
+            data = client.query(sql)
+            Hiera.debug("Mysql Query returned #{res.size} rows")
+          rescue => e
+            Hiera.debug e.message
+            data = nil
+          end
+
+          return data
+
+        end
+      end
+    end
+  end
+end