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copied!<p>There are a couple of ways you could do this. First, you could set up two <code>belongs_to</code>/<code>has_one</code> relationships:</p> <pre><code>things - bar:int - foo_id:int - goo_id:int whazits - content:string - value:int class Thing < ActiveRecord::Base belongs_to :foo, :class_name => "whazit" belongs_to :goo, :class_name => "whazit" end class Whazit < ActiveRecord::Base has_one :foo_owner, class_name => "thing", foreign_key => "foo_id" has_one :goo_owner, class_name => "thing", foreign_key => "goo_id" # Perhaps some before save logic to make sure that either foo_owner # or goo_owner are non-nil, but not both. end </code></pre> <p>Another option which is a little cleaner, but also more of a pain when dealing with plugins, etc., is single-table inheritance. In this case you have two classes, Foo and Goo, but they're both kept in the whazits table with a type column that distinguishes them.</p> <pre><code>things - bar:int whazits - content:string - value:int - thing_id:int - type:string class Thing < ActiveRecord::Base belongs_to :foo belongs_to :goo end class Whazit < ActiveRecord::Base # .. whatever methods they have in common .. end class Foo < Whazit has_one :thing end class Goo < Whazit has_one :thing end </code></pre> <p>In both cases you can do things like <code>@thing.foo</code> and <code>@thing.goo</code>. With the first method, you'd need to do things like:</p> <pre><code>@thing.foo = Whazit.new </code></pre> <p>whereas with the second method you can do things like:</p> <pre><code>@thing.foo = Foo.new </code></pre> <p>STI has its own set of problems, though, especially if you're using older plugins and gems. Usually it's an issue with the code calling <code>@object.class</code> when what they really want is <code>@object.base_class</code>. It's easy enough to patch when necessary.</p>

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