Is there a difference between the has_many , has_and_belongs_to_many and the polymorphic association. Why should I use polymorphic association.
has_many, has_and_belongs_to_many and the polymorphic associations are solutions to different problems.
has_many means you have a parent object that has many other children. While the children do only belong to that specific parent.has_and_belongs_to_many means the objects are not structured in a hierarchical structure. And that the objects on both sides can be connected to mutiple others. A good example is probably a tagging system. A thing can be tagged with multiple tags. But the tags do not only belong to one thing, they can be added to other things too.polymorphic associations are used when the association doesn't point to one specific other model. An example might be an Author model that has a created_work association, but it doesn't point to a decicated CreatedWork model. But instead, it can return different things, like an instance of a Book, a Play an Article, or a simple Comment which are all different classes and have different database tables.