如何在Ext中引用字段的内容？

Ext.define('MyApp.model.User', {
    extend: 'Ext.data.Model',
    fields: [
        'name', 'age', 'email'
    ]
});

var user = Ext.create('MyApp.model.User', {
    name: 'John',
    age: 25,
    email: 'john@example.com'
});

Ext.create('Ext.form.Panel', {
    title: 'User Details',
    items: [{
        xtype: 'textfield',
        fieldLabel: 'Name',
        bind: '{user.name}'
    }, {
        xtype: 'numberfield',
        fieldLabel: 'Age',
        bind: '{user.age}'
    }, {
        xtype: 'textfield',
        fieldLabel: 'Email',
        bind: '{user.email}'
    }],
    viewModel: {
        data: {
            user: user
        }
    },
    renderTo: Ext.getBody()
});