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copied!<p>The reason why your code is not working is simple - you are working with @content which is <code>nil</code> in the context of execution (the <code>self</code> is the class, not the instance). So you are basically modifying eigenclass of nil.</p> <p>So you need to extend the instance of @content when it's set. There are few ways, there is one:</p> <pre><code>class HtmlSnippet < ActiveRecord::Base # getter is overrided to extend behaviour of freshly loaded values def content value = read_attribute(:content) decorate_it(value) unless value.respond_to?(:replace_url_to_anchor_tag) value end def content=(value) dup_value = value.dup decorate_it(dup_value) write_attribute(:content, dup_value) end private def decorate_it(value) class << value def replace_url_to_anchor_tag # ... end end end end </code></pre> <p>For the sake of simplicity I've ommited the "nil scenario" - you should handle <code>nil</code> values differently. But that's quite simple.</p> <p>Another thing is that you might ask is why I use <code>dup</code> in the setter. If there is no <code>dup</code> in the code, the behaviour of the following code might be wrong (obviously it depends on your requirements):</p> <pre><code>x = "something" s = HtmlSnippet.find(1) s.content = x s.content.replace_url_to_anchor_tag # that's ok x.content.replace_url_to_anchor_tag # that's not ok </code></pre> <p>Wihtout <code>dup</code> you are extending not only x.content but also original string that you've assigned.</p>

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