instance method method_missing

# File activerecord/lib/active_record/database_configurations.rb, line 201
      def method_missing(method, *args, &blk)
        case method
        when :fetch
          throw_getter_deprecation(method)
          configs_for(env_name: args.first)
        when :values
          throw_getter_deprecation(method)
          configurations.map(&:config)
        when :[]=
          throw_setter_deprecation(method)

          env_name = args[0]
          config = args[1]

          remaining_configs = configurations.reject { |db_config| db_config.env_name == env_name }
          new_config = build_configs(env_name => config)
          new_configs = remaining_configs + new_config

          ActiveRecord::Base.configurations = new_configs
        else
          raise NotImplementedError, "`ActiveRecord::Base.configurations` in Rails 6 now returns an object instead of a hash. The `#{method}` method is not supported. Please use `configs_for` or consult the documentation for supported methods."
        end
      end