使用 Backbone.js 轮询集合

Question

我正在尝试使 Backbone.js 集合与服务器上发生的事情保持同步。

我的代码类似如下：

var Comment = Backbone.Model.extend({});
var CommentCollection = Backbone.Collection.extend({
    model: Comment
});

var CommentView = Backbone.View.extend({ /* ... */ });
var CommentListView = Backbone.View.extend({
    initialize: function () {
        _.bindAll(this, 'addOne', 'addAll');

        this.collection.bind('add', this.addOne);
        this.collection.bind('refresh', this.addAll);
    },
    addOne: function (item) {
        var view = new CommentView({model: item});
        $(this.el).append(view.render().el);
    },
    addAll: function () {
        this.collection.each(this.addOne);
    }
});

var comments = new CommentCollection;
setInterval(function () {
    comments.fetch();
}, 5000);

当获取 cmets 时，refresh 被调用，CommentListView 底部的相同 cmets - 这是我对上面代码的期望。

我想知道在不丢失任何“本地状态”的情况下“刷新”视图的最佳方式是什么。

Answer 1

或者只是使用简单得多的附加到主干的 fetch 方法：

this.fetch({ update: true });

当模型数据从服务器返回时，集合将（有效地）重置，除非您传递 {update: true}，在这种情况下，它将使用 update 来（智能地）合并获取的模型。 - Backbone Documentation

:-)

Answer 2

Backbone.Collection.merge([options])

基于@Jeb 的上述回复，我已将此行为封装到 Backbone 扩展中，您可以将其复制并粘贴到 .js 文件中并包含在您的页面中（在包含 Backbone 库本身之后）。

它为 Backbone.Collection 对象提供了一个名为 merge 的方法。它不是完全重置现有集合（如fetch 所做的那样），而是将服务器响应与现有集合进行比较并合并它们的差异。

1. 它添加响应中的模型，但不在现有集合中。
2. 它删除现有集合中但不在响应中的模型。
3. 最后，它更新在现有集合和响应中找到的模型的属性。

为添加、删除和更新模型触发所有预期事件。

options 哈希将success 和error 回调作为参数传递给(collection, response)，它提供了第三个回调选项complete，无论成功或失败都会执行错误（主要用于轮询场景）。

它触发名为“merge:success”和“merge:error”的事件。

这是扩展名：

// Backbone Collection Extensions
// ---------------

// Extend the Collection type with a "merge" method to update a collection 
// of models without doing a full reset.

Backbone.Collection.prototype.merge = function(callbacks) {
    // Make a new collection of the type of the parameter 
    // collection.
    var me = this;
    var newCollection = new me.constructor(me.models, me.options);
    this.success = function() { };
    this.error = function() { };
    this.complete = function() { };

    // Set up any callbacks that were provided
    if(callbacks != undefined) {
        if(callbacks.success != undefined) {
            me.success = callbacks.success;
        }

        if(callbacks.error != undefined) {
            me.error =  callbacks.error;
        }

        if(callbacks.complete != undefined) {
            me.complete = callbacks.complete;
        }
    }

    // Assign it the model and url of collection.
    newCollection.url = me.url;
    newCollection.model = me.model;

    // Call fetch on the new collection.
    return newCollection.fetch({
        success: function(model, response) {
            // Calc the deltas between the new and original collections.
            var modelIds = me.getIdsOfModels(me.models);
            var newModelIds = me.getIdsOfModels(newCollection.models);

            // If an activity is found in the new collection that isn't in
            // the existing one, then add it to the existing collection.
            _(newCollection.models).each(function(activity) {
                if (_.indexOf(modelIds, activity.id) == -1) { 
                    me.add(activity);
                }
            }, me);

            // If an activity in the existing collection isn't found in the
            // new one, remove it from the existing collection.
            var modelsToBeRemoved = new Array();
            _(me.models).each(function(activity) {
                if (_.indexOf(newModelIds, activity.id) == -1) {  
                    modelsToBeRemoved.push(activity);
                }
            }, me);
            if(modelsToBeRemoved.length > 0) {
                for(var i in modelsToBeRemoved) {
                    me.remove(modelsToBeRemoved[i]);
                }
            }

            // If an activity in the existing collection is found in the
            // new one, update the existing collection.
            _(me.models).each(function(activity) {
                if (_.indexOf(newModelIds, activity.id) != -1) { 
                    activity.set(newCollection.get(activity.id));  
                }
            }, me);

            me.trigger("merge:success");

            me.success(model, response);
            me.complete();
        },
        error: function(model, response) {
            me.trigger("merge:error");

            me.error(model, response);
            me.complete();
        }
    });
};

Backbone.Collection.prototype.getIdsOfModels = function(models) {
        return _(models).map(function(model) { return model.id; });
};

简单使用场景：

var MyCollection = Backbone.Collection.extend({
  ...
});
var collection = new MyCollection();
collection.merge();

错误处理使用场景：

var MyCollection = Backbone.Collection.extend({
  ...
});

var collection = new MyCollection();

var jqXHR = collection.merge({
    success: function(model, response) {
        console.log("Merge succeeded...");
    },
    error: function(model, response) {
        console.log("Merge failed...");
        handleError(response);
    },
    complete: function() {
        console.log("Merge attempt complete...");
    }
});

function handleError(jqXHR) {
    console.log(jqXHR.statusText);

    // Direct the user to the login page if the session expires
    if(jqXHR.statusText == 'Unauthorized') {
        window.location.href = "/login";                        
    }
};

Answer 3

制作一个重复的集合。获取（）它。比较两者以找到增量。应用它们。

      /*
       * Update a collection using the changes from previous fetch,
       * but without actually performing a fetch on the target 
       * collection. 
       */
      updateUsingDeltas: function(collection) {
        // Make a new collection of the type of the parameter 
        // collection.
        var newCollection = new collection.constructor(); 

        // Assign it the model and url of collection.
        newCollection.url = collection.url;
        newCollection.model = collection.model;

        // Call fetch on the new collection.
        var that = this;
        newCollection.fetch({
          success: function() {
            // Calc the deltas between the new and original collections.
            var modelIds = that.getIdsOfModels(collection.models);
            var newModelIds = that.getIdsOfModels(newCollection.models);

            // If an activity is found in the new collection that isn't in
            // the existing one, then add it to the existing collection.
            _(newCollection.models).each(function(activity) {
              if (modelIds.indexOf(activity.id) == -1) { 
                collection.add(activity);
              }
            }, that);

            // If an activity in the existing colleciton isn't found in the
            // new one, remove it from the existing collection.
            _(collection.models).each(function(activity) {
              if (newModelIds.indexOf(activity.id) == -1) {  
                collection.remove(activity);  
              }
            }, that);

            // TODO compare the models that are found in both collections,
            // but have changed. Maybe just jsonify them and string or md5
            // compare.
          }
        });
      },

      getIdsOfModels: function(models) {
        return _(models).map(function(model) { return model.id; });
      },

Answer 4

您想要做的是每隔几秒刷新一次集合并附加新的 cmets。我的建议是在你的后端处理这个问题。发送您上次评论的最后一个时间戳，并仅向服务器询问该日期的增量。

为此，请在您的收藏中：

CommentCollection = Backbone.Collection.extend({
  url: function(){
    return "/comments?from_time=" + this.last().get("created_at");
  },
  comparator: function(comment){
    return comment.get("created_at");
  }
});

在您的后端，根据 from_time 参数查询您的数据库。您的客户端代码不会更改以刷新视图。

如果您出于任何原因不想更改后端代码，请在 addAll 函数中添加此行：

addAll: function(){
  $(this.el).empty();
  this.collection.each(this.addOne);
}