title: Magento backend_model - do I need to specify for each config field?
body: <p>If I want to do something extra when a particular configuration field for my custom module is saved  (over and above saving to the Magento core config table), I can just specify a backend_model for that field in my system.xml, and have that backend model class extend Mage_Core_Model_Config_Data, override _afterSave, and put my extra stuff in that method.</p>
  
  <p>But what if I have several fields I want to do this for. I don't want the behaviour to be to save field1 and call my afterSave for that field, save field2 and call my afterSave for that field, etc. I'd rather that all the fields were saved to the Magento core config table, and then I do my extra stuff.</p>
  
  <p>Is that possible? I thought I might be able to achieve that using event/observer. So in my config.xml, &lt;adminhtml&gt; section, I added an observer as follows:</p>
  
  <pre><code>&lt;events&gt;
      &lt;admin_system_config_changed_mysection&gt;
          &lt;observers&gt;
              &lt;mypfx_admin_system_config_changed_mysection&gt;
                  &lt;class&gt;mymodule/adminhtml_system_config_backend_configSaveObserver&lt;/class&gt;
                  &lt;method&gt;myConfigSaved&lt;/method
              &lt;/mypfx_admin_system_config_changed_mysection&gt;
          &lt;/observers&gt;
      &lt;/admin_system_config_changed_mysection&gt;    
  &lt;/events&gt;
  </code></pre>
  
  <p>but my observer method is not called when the config is saved. Maybe I have the wrong event name? The "mysection" bit on the end of the event name I was guessing had to match the section from system.xml:</p>
  
  <pre><code>&lt;sections&gt;    
      &lt;mysection translate="label" module="mymodule"&gt;
          ...
          &lt;groups&gt;
              ...
          &lt;/groups&gt;
      &lt;/mysection&gt;
  &lt;/sections&gt;
  </code></pre>
  
  <p>Thanks.</p>