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POhas_many :through -- Adding metadata to the through relationship
 

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    <p>I have a need to add metadata about a HABTM relationship. I wanted to use a has_many :through relationship to accomplish this, but it is not necessary. Here is the problem simplified:</p> <pre><code>class Customer &lt; ActiveRecord::Base has_many :customer_teddy_bears has_many :teddy_bears, :through =&gt; :customer_teddy_bears end class CustomerTeddyBear &lt; ActiveRecrod::Base belongs_to :customer belongs_to :teddy_bear attr_accesible :most_favoritest # just to show it exists, boolean end class TeddyBear &lt; ActiveRecord::Base has_many :cusomter_teddy_bears end </code></pre> <p>So what I need to do is start adding teddy bears to my customers, Teddy Bears are a fixed set of data, lets say a fireman_bear, doctor_bear, dominatrix_bear. Any customer can claim to own a kind of teddy bear, but they also specify which is their most favoritest bear. Since I cannot modify the bears model because that is globally shared among all customers I am adding the metadata (among other metadata) to CustomerTeddyBear.</p> <p>The problem is that the following does not work.</p> <pre><code>customer = Customer.new # new record, not yet saved, this must be handled. customer.teddy_bears &lt;&lt; fireman_bear customer.teddy_bears &lt;&lt; doctor_bear # now to set some metadata favoritest_record = customer.customer_teddy_bears.select{|ctb| ctb.teddy_bear == doctor_bear}.first favoritest_record.most_favoritest = true </code></pre> <p>The above code does not work since customer_teddy_bears entries are only populated during save when creating records in the database. Is there another mechanism for doing this?</p> <p>If there is nothing "automated" built into rails I will just have to manually manage this relationship by including <code>teddy_bears</code> when I select <code>customer_teddy_bears</code> and using techniques like </p> <pre><code>def teddy_bears self.customer_teddy_bears.map(&amp;:teddy_bear) end </code></pre> <p>along with manually creating the associations, and not using a :through relationship.</p> <p>please note, all this must happen before the <code>#save</code> is executed on the <code>Customer</code> object, so I need to set all relevant metadata while still in-memory.</p> <p>Recommendations I got from #RubyOnRails</p> <pre><code>ctb = customer.customer_teddy_bears.build({:customer =&gt; customer, :teddy_bear =&gt; fireman_bear}) ctb2 = customer.customer_teddy_bears.build({:customer =&gt; customer, :teddy_bear =&gt; doctor_bear}) ... ctb.most_favoritest = true </code></pre>
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