One of the most powerful aspects of Ruby on Rails are the associations we can create between two classes. It is immensely convenient to be able to call person.posts rather than doing a SQL statement to find all of the posts with a person_id of X.

Sometimes, we have instances where the associations could be with multiple classes. For example, if we have a Page class that can be associated with an HTMLAdvertisement or an ImageAdvertisement. In that case, we really want to be able to call @page.advertisement to get the advertisement. This is where polymorphic associations come in.

Polymorphic associations allow us to associate a single attribute of the class to any number of specified classes. Here are the Page, HtmlAdvertisement, and ImageAdvertisement models:

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activerecord, Database, migration, mixin modules, polymorphic associations, restful routes