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Add note about inheretance and poly associations.

This note came about due to discussion in #6786.
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1 parent f5654e7 commit e9acafd984ef64b44a8f0c998acaddbdce1dd6fb @steveklabnik steveklabnik committed Sep 17, 2012
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  1. +4 −0 guides/source/association_basics.textile
@@ -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:

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