```ruby
require 'fog/core/model'

module Fog
  module AWS
    class RDS

      class SubnetGroup < Fog::Model

        identity   :id, :aliases => ['DBSubnetGroupName', :name]
        attribute  :description, :aliases => 'DBSubnetGroupDescription'
        attribute  :status, :aliases => 'SubnetGroupStatus'
        attribute  :vpc_id, :aliases => 'VpcId'
        attribute  :subnet_ids, :aliases => 'Subnets'

        # TODO: ready?
        #
        def save
          requires :description, :id, :subnet_ids
          service.create_db_subnet_group(id, subnet_ids, description)
          reload
        end

        def destroy
          requires :id
          service.delete_db_subnet_group(id)
        end

      end
    end
  end
end
```

Implement `ready?` for subnet group.
user
```ruby
require 'fog/core/model'

module Fog
  module AWS
    class RDS

      class SubnetGroup < Fog::Model

        identity   :id, :aliases => ['DBSubnetGroupName', :name]
        attribute  :description, :aliases => 'DBSubnetGroupDescription'
        attribute  :status, :aliases => 'SubnetGroupStatus'
        attribute  :vpc_id, :aliases => 'VpcId'
        attribute  :subnet_ids, :aliases => 'Subnets'

        def ready?
          requires :status
          status == 'Complete'
        end

        def save
          requires :description, :id, :subnet_ids
          service.create_db_subnet_group(id, subnet_ids, description)
          reload
        end

        def destroy
          requires :id
          service.delete_db_subnet_group(id)
        end

      end
    end
  end
end
```
assistant