title: ExtJS: store - proxy - writer: how to always add/set a value to records when sync?
body: <p>After two days of struggling, I've made my own <code>Ext.data.Store</code> class that works (see code below).</p>
  
  <p>Note that, even though all the configuration of the proxy and its writer are taken in account, the configuration <code>writeAllFields: true</code> is ignored and only the changed values are sent (which is a big problem to me).</p>
  
  <p>So, now, to circumvent that (huge) problem, I'd like to <strong>always</strong> add a pre-defined value to the records that are sent (it's always one value, something like <code>id_partner: 3</code>). I need this for security reasons.</p>
  
  <pre><code>Ext.define('Ext.data.StoreHandleErrors', {
      extend: 'Ext.data.Store',
      alias: 'data.storehandleerrors',
  
      constructor: function(config) {
          config.autoLoad= true;
          config.autoSync= true;
          config.proxy.type= 'ajax';
          config.proxy.reader= {
              type: 'json',
              successProperty: 'success',
              root: 'data',
              messageProperty: 'message'
          };
          config.proxy.writer= {
              type: 'json',
              writeAllFields: true,
              root: 'data'
          };
          config.proxy.listeners= {
  
              exception: function(proxy, response, operation) {
                  /* Code to handle exception */
              }
          };
          this.callParent([config]);
          this.on(
              'write',
              function(store, operation) {
                  /* Code to show how the write op. went */
              },
              this
          );
          this.on(
              'beforesync',
              function(objects_to_sync, opts) {
                  /* Code to add a pre-defined value to be sent: "id_partner: 3" */
              },
              this
          );
      }
  });
  </code></pre>
  
  <p>Any idea how I could do this?</p>