resolve

# File activerecord/lib/active_record/connection_adapters.rb, line 26
      def resolve(adapter_name) # :nodoc:
        # Require the adapter itself and give useful feedback about
        #   1. Missing adapter gems.
        #   2. Incorrectly registered adapters.
        #   3. Adapter gems' missing dependencies.
        class_name, path_to_adapter = @adapters[adapter_name.to_s]

        unless class_name
          raise AdapterNotFound, <<~MSG.squish
            Database configuration specifies nonexistent '#{adapter_name}' adapter.
            Available adapters are: #{@adapters.keys.sort.join(", ")}.
            Ensure that the adapter is spelled correctly in config/database.yml and that you've added the necessary
            adapter gem to your Gemfile if it's not in the list of available adapters.
          MSG
        end

        unless Object.const_defined?(class_name)
          begin
            require path_to_adapter
          rescue LoadError => error
            # We couldn't require the adapter itself.
            if error.path == path_to_adapter
              # We can assume here that a non-builtin adapter was specified and the path
              # registered by the adapter gem is incorrect.
              raise LoadError, "Error loading the '#{adapter_name}' Active Record adapter. Ensure that the path registered by the adapter gem is correct. #{error.message}", error.backtrace
            else
              # Bubbled up from the adapter require. Prefix the exception message
              # with some guidance about how to address it and reraise.
              raise LoadError, "Error loading the '#{adapter_name}' Active Record adapter. Missing a gem it depends on? #{error.message}", error.backtrace
            end
          end
        end

        begin
          Object.const_get(class_name)
        rescue NameError => error
          raise AdapterNotFound, "Could not load the #{class_name} Active Record adapter (#{error.message})."
        end
      end