Javascript ExtJS4JSON树存储？

我正在将ExtJs3应用程序迁移到ExtJs4。
在ExtJs3中，我有一个树网格，它有一个加载程序来加载树数据，如下所示：

loader: new Ext.tree.TreeLoader({ 
            dataUrl: 'Department/DepartmentTree', 
            nestedRoot: 'Data.items'
    })

   var store = Ext.create('Ext.data.TreeStore', {
        model: 'DepartmentTreeModel',
        folderSort: true,
        proxy: {
            type: 'ajax',
            url: 'Department/DepartmentTree',
            reader: {
                type: 'json',
                root: 'Data.items'
            }
        }
    });

因此，我尝试在ExtJs4中创建一个树存储，如下所示：

loader: new Ext.tree.TreeLoader({ 
            dataUrl: 'Department/DepartmentTree', 
            nestedRoot: 'Data.items'
    })

   var store = Ext.create('Ext.data.TreeStore', {
        model: 'DepartmentTreeModel',
        folderSort: true,
        proxy: {
            type: 'ajax',
            url: 'Department/DepartmentTree',
            reader: {
                type: 'json',
                root: 'Data.items'
            }
        }
    });

调用上述存储的load函数时出错

无法读取未定义的
的属性“items”

JSON响应如下所示：

    {
"Data":{
    "__type":"ListWrapperOfDepartmentTreeNodewnEzJCii:#PortalMvc.Global.Classlibrary.Model.Ui.JSONWrappers",
    "items":[{
        "ActualHeadcount":0,
        "Headcount":0,
        "Leavers":0,
        "ParentId":"~~",
        "Starters":0,
        "children":[{
            "ActualHeadcount":0,
            "Headcount":0,
            "Leavers":0,
            "ParentId":"!#",
            "Starters":0,
            "children":[{
                "ActualHeadcount":0,
                "Headcount":0,
                "Leavers":0,
                "ParentId":"*w",
                "Starters":0,
                "children":[{
                    "ActualHeadcount":0,
                    "Headcount":0,
                    "Leavers":0,
                    "ParentId":"*z",
                    "Starters":0,
                    "children":[],
                    "iconCls":"admin_button",
                    "id":"*{",
                    "leaf":true,
                    "text":"Parking1_subtree1"
                }]
            }]
        }]
    }]
  }
}

它期望为每一组子节点重复根节点。所以对于“儿童”，它也尝试读取“Data.items”

如果无法更改数据结构，则根也可以是一个函数，类似于：

root: function(o) {
    if (o.Data) {
        return o.Data.items;
    } else {
        return o.children;
    }
}