Support non-standard foreign key types (e.g. Rails "Polymorphic Associations" or Hibernate "Discriminator Column STI")

[bluerogue251]

I'm opening this issue to see how much demand there is for a feature that would support certain types of non-standard Foreign Keys. Examples of this include:

• Rails Polymorphic Associations: http:https://guides.rubyonrails.org/association_basics.html#polymorphic-associations
• Hibernate "Discriminator Column Single Table Inheritance": http:https://docs.jboss.org/hibernate/orm/5.2/userguide/html_single/Hibernate_User_Guide.html#entity-inheritance-single-table (search for "discriminator")

If you would like such a feature please add a 👍 to this issue, and feel free to leave any specific notes about your use case in this thread.