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Add note about inheretance and poly associations.

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This note came about due to discussion in #6786.
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Steve Klabnik 2012-09-17 22:03:34 +03:00
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@ -338,6 +338,10 @@ end
!images/polymorphic.png(Polymorphic Association Diagram)!
Polymorphic associations can get tricky with inheritance. If you need
an inheritance relationship in your ActiveRecord models, you should use
Single Table Inheritance instead.
h4. Self Joins
In designing a data model, you will sometimes find a model that should have a relation to itself. For example, you may want to store all employees in a single database model, but be able to trace relationships such as between manager and subordinates. This situation can be modeled with self-joining associations: