title: From an extjs combobox for Rally builds, how do I fetch a field on the child ChangeSets records?
body: <p>Using SDK 2, I created a combobox that lets me select a build.  I have a listener that wants to do something with the array of ChangeSets, but the array is only returning the attribute information (ref, etc). In the olden days, I could fetch the fields I wanted on a parent and see them in the children, too.  So, how do I get the ChangeSets to provide a Revision, say?</p>
  
  <p>Here is the definition of the combobox:</p>
  
  <pre><code>this.down('#buildSelector').add({
          xtype: 'rallycombobox',
          displayField: 'Number',
          listeners: {
              scope: this,
              select: function(combo, records, eOpts){
                  this._buildResults(combo.getRecord().data);//Build
              },
              ready: function(combo, records, eOpts){
                  this._buildResults(combo.getRecord().data);//Build
              }
          },
          width: 280,   
          storeConfig: {
              autoLoad: true,
              model: 'Build',
              pagesize: 20, //# of builds displayed in drop down
               sorters: [{
                          property: 'CreationDate',
                          direction: 'DESC'
                        }],
  
              listeners: {
                  load: function(store, records, successful){
                          console.log("dropdown records", records);
                      }
                  }
              }
      });
  </code></pre>
  
  <p>That console log gives me something like this</p>
  
  <pre><code>dropdown records 
    Array[200]
      [0 … 13]
        0: Ext.Class.newClass
          data: Object
          BuildDefinition: Object
          Changesets: Array[2]
            0: Object
              _rallyAPIMajor: "1"
              _rallyAPIMinor: "31"
              _ref: "https://audemo.rallydev.com/slm/webservice/1.31/changeset/1260800.js"
              _refObjectName: "BuildHealthReportRepo:1000"
              _type: "Changeset"
              __proto__: Object
            1: Object
  </code></pre>
  
  <p>etc...</p>