On my site everything can be commented (videos, articles, posts, other comments, whatever), 14 different models. All comments are governed by Comment model. The question is: how do I specify association between Comment and all other models? Adding 14 foreign keys is definitely not an option, same as bunch of intermediary tables. Also please note that I don’t want to make a virtual relation (make get/setComments methods for each model or through behavior with own code that’ll load/save comments).
If you want cascade deleting (deleting a video will delete the comments) you have 2 options:
the simpliest is to add 14 fk, no preformance concerns, noone cares.
make specification of table:
a table ‘commentable’ with at least the only id
comments has a fk on commentable
all your entities has a fk on commentable
eg: video: id, commentable_id, other fields.
In this way you have to delete the related commentable for cascade deleting all records, also the comment, deletecomment action will work on the same model, wich simplifies a lot.
I can say only that this solution is definitely a dirty hack. Thanks for responses people.