paperclip - Rails STI conditional sub-classing from base class -

i'm developing project have entity may have 2 kinds of assets: pictures , videos, basically.

since want assets on same table , single upload form either pictures or videos, i'm using single table inheritance having both picture , video descending asset class. also, i'll running different validations/callbacks depending on whether video or picture.

i'm using paperclip deal upload process, , idea when uploading file , creating asset it, application instantiate correct subclass (picture or video) depending on mime-type of uploaded file.

this sketch of classes:

class project < activerecord::base   has_many :assets   accepts_nested_attributes_for :assets end  class asset < activerecord::base   belongs_to :project   has_uploaded_file :content, ... end  class picture < asset   validate :image_size   ... end  class video < asset   after_save :convert_format   ... end 

my idea implement before_save callback on asset class , try instantiate correct class there, i'm not sure how or if it's idea.

any idea this?

while should favor fat models , skinny controllers, me seems better placed in controller. primary rationale doing in asset model coupling base type subtypes, doesn't feel right me (although see apis time).