title: How to write to a memoryproxy in Ext.js
body: <p>I'm trying to use Extjs with a javascript view model. I've had success with loading stores using a JsonReader and the ext.data.memoryproxy class.</p>
  
  <p>However I want to write changes to my Javascript viewmodel.I tried adding a jsonwriter to the writer property of the store but this doesn't work. I get this error:</p>
  
  <blockquote>
    <p>uncaught exception: Ext.data.DataProxy: DataProxy attempted to execute an API-action but found an undefined url / function.  Please review your Proxy url/api-configuration.</p>
  </blockquote>
  
  <p>My Code is:</p>
  
  <pre><code>var service = viewmodel.selectedService.analytes;
  
       var serviceResultsStore = new Ext.data.Store({
          reader: new Ext.data.JsonReader({
              fields: ['Analyte', 'Units', 'Value', 'Rounded', 'PossibleValues']
  
          }),
          proxy: new Ext.data.MemoryProxy(service),
             writer: new Ext.data.JsonWriter({
                      encode: false,
                      writeAllFields:true
                  })
  </code></pre>
  
  <p>Any Help on this would be greatly appreciated!</p>