polymorphic features of avram.

[zw963]

I am current want to use polymorphic feature of avram, I expected it works as this PR, but I never found a method/macro defined named add_polymorphic in migration.

I saw our doc in https://luckyframework.org/guides/database/models#polymorphic-associations, but it not explain what is the underearth table columns.

Are we not supporting something similar to how polymorphic column are managed in Rails, e.g. described in above #150 and #145

Do

add_polymorphic commentable

Instead of:

  add commentable_type : String?
  add commentable_id : Int32?

Thanks

[jwoertink]

The polymorphic feature for Avram requires that you define each column separately. It doesn't work like using STI where you have a type and id columns because in ruby you can do "Post".constantize.find(commentable_id), but in Crystal there's not a way to "constantize", so you have to know the type at compiletime.