json - 收集上的骨干更改事件，为什么它有效？

Question

为什么事件“更改”适用于模型评论 1？怎么修？如果我删除行（'comment'：[]），事件'change'不起作用。我明白这是因为我使用数组，但我需要使用它，但我没有事件，如果他没有任何变化。谢谢/

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创建新集合

var commentCollection = new VPRS.Comment.CommentCollection([
  {
    "id": "comment1",
    "questionId": "post1",
    "name": "Alex",
    "text": "text 1",
    "comment":[]
  },
  {
    "id": "comment2",
    "questionId": "post1",
    "name": "Alex",
    "text": "Text2"
  }
]);


----------

    json = [
      {
        "id": "comment1",
        "questionId": "post1",
        "name": "Alex",
        "text": "text 1",
        "comment":[]
      },
      {
        "id": "comment2",
        "questionId": "post1",
        "name": "Alex",
        "text": "Text2"
     }]

--------------
wallItemCollection.on('change', function (model) {
  console.log('model change')
}
 ------------
wallItemCollection.fetch({
  update: true,
  merge: true,
  success: function () {
    console.log('fetch compleate')
  }
});