resolve_hash_connection

# File activerecord/lib/active_record/connection_adapters/connection_specification.rb, line 49
        def resolve_hash_connection(spec) # :nodoc:
          spec = spec.symbolize_keys

          raise(AdapterNotSpecified, "database configuration does not specify adapter") unless spec.key?(:adapter)

          path_to_adapter = "active_record/connection_adapters/#{spec[:adapter]}_adapter"
          begin
            require path_to_adapter
          rescue Gem::LoadError => e
            raise Gem::LoadError, "Specified '#{spec[:adapter]}' for database adapter, but the gem is not loaded. Add `gem '#{e.name}'` to your Gemfile."
          rescue LoadError => e
            raise LoadError, "Could not load '#{path_to_adapter}'. Make sure that the adapter in config/database.yml is valid. If you use an adapter other than 'mysql', 'mysql2', 'postgresql' or 'sqlite3' add the necessary adapter gem to the Gemfile.", e.backtrace
          end

          adapter_method = "#{spec[:adapter]}_connection"

          ConnectionSpecification.new(spec, adapter_method)
        end