old_contents: App.cfg.modelChatUser = {
      url: '/um/lib/chat/user',
      fields:[
      {
          name: 'id',
          type: 'string',
          persist: false
      }
      ],
      columns:[
      {
          dataIndex:'id',
          flex: 1
      }
      ]
  }
  
  Ext.define('App.model.userman.chatUser',{
      extend: App.model.BaseCRUD,
      fields: App.cfg.modelChatUser.fields
  })
  
new_contents: App.cfg.modelChatUser = {
      url: '/um/lib/chat/user',
      fields:[
      {
          name: '_id',
          type: 'string'
      }
      ],
      columns:[
      {
          dataIndex: '_id',
          flex: 1
      }
      ]
  }
  
  Ext.define('App.model.userman.chatUser',{
      extend: App.model.BaseCRUD,
      fields: App.cfg.modelChatUser.fields
  })
  
subject: use CRUD model's ID === _id as id