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    <p>because then your Favorite instance will not know what it is favouriting :) it knows that it <code>has_one :note</code>, but also has_one <code>:comment</code>, or? but not both surely.</p> <p><strong>polymorphic association the opposite way</strong> helps because it will express that a <code>Favorite</code> object belongs_to <code>:favorited</code> object that is polymorphic cos it can be any class the name of which will be stored in the <code>:favorited_type</code> string db column, so your favorite object will know that it favors a note or document or comment.</p> <p>with some code</p> <pre><code>class Note has_many :favorites, :as =&gt; :favorited has_many :fans, :through =&gt; :favorites, :source =&gt; :user end class Discussion has_many :favorites, :as =&gt; :favorited has_many :fans, :through =&gt; :favorites, :source =&gt; :user end class Comment has_many :favorites, :as =&gt; :favorited has_many :fans, :through =&gt; :favorites, :source =&gt; :user end class Favorite belongs_to :user belongs_to :favorited, :polymorphic =&gt; true # note direction of polymorphy end class User has_many :favorites has_many :favorite_notes, :through =&gt; :favorites, :source =&gt; favorited, :source_type =&gt; "Note" has_many :favorite_comments, :through =&gt; :favorites, :source =&gt; favorited, :source_type =&gt; "Comment" has_many :favorite_discussions, :through =&gt; :favorites, :source =&gt; favorited, :source_type =&gt; "Discussion" end </code></pre> <p>(just set up your db correctly) this design is standard for such usecase of favoriting.</p>
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    1. POWhat do polymorphic associations solve?
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    1. COI'm not sure I follow. What problem does a polymorphic association solve? And if you can, please describe your answer in the context of my example (unless my example does not relate, in which case, what example does?). Thank you.
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    2. COI think I did explain in the context of your example exactly. I added some code, hope it helps.
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    3. COAs I said, I'm not sure I follow with respects to your answer fitting my question. Once again, what problem does a polymorphic association solve?
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