gistfile1.txt

var FactoryForm = function() {

   var form = new Ext.form.FormPanel({

   width: 400, height: 150, frame: true
   , defaults : {
     margins: {top:15, right:0, bottom:0, left:5}
   }
   , defaultType: "textfield"
   , items: [

       {name:"nome",  fieldLabel : "Nome"}
       , {name:"descricao",  fieldLabel : "Descrição"}
       ,  {xtype: "datefield", name:"created_at",  fieldLabel : "Data Criação"}
       , {xtype: "hidden", name: "id"}

    ]

   });

   return form;
};

var instrutor = function(json, record) {
  var nome = "";
  record.instrutores.forEach(function(inst){ nome += (inst.nome + ", ") });
  return nome;
}

var CursoFactory = Ext.data.Record.create(["id", "nome", "descricao",
{name:"instrutores", convert: instrutor}]);

var store = new Ext.data.Store({
    url: "/cursos.json",
    reader: new Ext.data.JsonReader({
        id: "id", root: "results", total: "total"
    }, CursoFactory)
})
store.load();

var grid = new Ext.grid.GridPanel({
  store: store
   , colModel: new Ext.grid.ColumnModel({
      columns: [
        {id:"id", header: "Id", width: 20, sortable: true, dataIndex: "id"}
        , {header: "Nome", width: 200, sortable: true, dataIndex: "nome"}
        , {header: "Descrição", width: 200, sortable: true, dataIndex: "descricao"}
        , {header: "Instrutores", width: 200, sortable: true, dataIndex: "instrutores"}
      ]
   })
   , sm: new Ext.grid.RowSelectionModel()
   , title: "Cursos", width: 600, height: 300, frame: true
   , listeners: {
        rowdblclick : function( grid, rowIndex, event ) {
            var rec = grid.getSelectionModel().getSelected();
            var win = new Ext.Window({
                 modal:true, title: "Curso", width: 300, height: 177, 
                 items:[new FactoryForm()]
            });
            win.show();
            win.items.get(0).getForm().loadRecord(rec);
        }
   }
   , style: "margin: auto;"
});
grid.render("treinamento");