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POModules vs. Classes and their influence on descendants of ActiveRecord::Base
 

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  1. POModules vs. Classes and their influence on descendants of ActiveRecord::Base
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    <p>Here's a Ruby OO head scratcher for ya, brought about by this Rails scenario: </p> <pre><code>class Product &lt; ActiveRecord::Base has_many(:prices) # define private helper methods end module PrintProduct attr_accessor(:isbn) # override methods in ActiveRecord::Base end class Book &lt; Product include PrintProduct end </code></pre> <p><code>Product</code> is the base class of all products. Books are kept in the <code>products</code> table via STI. The <code>PrintProduct</code> module brings some common behavior and state to descendants of <code>Product</code>. <code>Book</code> is used inside <code>fields_for</code> blocks in views. This works for me, but I found some odd behavior:</p> <ul> <li>After form submission, inside my controller, if I call a method on a book that is defined in <code>PrintProduct</code>, and that method calls a helper method defined in <code>Product</code>, which in turn calls the <code>prices</code> method defined by <code>has_many</code>, I'll get an error complaining that <code>Book#prices</code> is not found.</li> </ul> <p>Why is that? Book is a direct descendant of Product! </p> <p>More interesting is the following..</p> <p>As I developed this hierarchy <code>PrintProduct</code> started to become more of an abstract <code>ActiveRecord::Base</code>, so I thought it prudent to redefine everything as such:</p> <pre><code>class Product &lt; ActiveRecord::Base end class PrintProduct &lt; Product end class Book &lt; PrintProduct end </code></pre> <p>All method definitions, etc. are the same. In this case, however, my web form won't load because the attributes defined by <code>attr_accessor</code> (which are "virtual attributes" referenced by the form but not persisted in the DB) aren't found. I'll get an error saying that there is no method <code>Book#isbn</code>. Why is that?? I can't see a reason why the <code>attr_accessor</code> attributes are not found inside my form's <code>fields_for</code> block when <code>PrintProduct</code> is a class, but they are found when <code>PrintProduct</code> is a <code>Module</code>. </p> <p>Any insight would be appreciated. I'm dying to know why these errors are occurring! </p>
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    1. COever figure this out? I am running into during my rails 3 port.
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      1. USchrishomer
 

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