During my application I've polymorphic idea model that we am using with various entity like project,chance etc. In idea table it classified using ideable_id &lifier ideable_type
E.G.- For Project ideable_id is project_id &lifier ideable_type is 'Project' E.G.- For Chance ideable_id is chance_id &lifier ideable_type is 'Opportunity'

Now my real question is that I must create idea for ideabank &lifier ideabank isn't entity like project or chance it is a virtual entity. just how must i create model without databsase that will produce ideable_id &lifier ideable_type? or while adding idea to ideabank will i bare this two column blank?