使用Backbone.js輪詢集合

Question

我正在努力使Backbone.js Collection與服務器上發生的事情保持同步。

我的代碼類似於以下內容：

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);

會發生什么事情，當提取注釋時，調用refresh ，注釋到CommentListView底部的相同注釋 - 這是我對上面代碼的期望。

我想知道的是什么是“刷新”視圖的最佳方式，而不會失去任何“本地狀態”。

Answer 1

或者只是使用更簡單的添加到backbone的fetch方法：

this.fetch({ update: true });

當模型數據從服務器返回時，集合將被（有效地）重置，除非您傳遞{update：true}，在這種情況下，它將使用update（智能地）合並獲取的模型。 - 骨干文檔

:-)

Answer 2

你想要做的是每隔幾秒刷新一次這個集合並添加新的評論。 我的建議是在你的后端處理這個問題。 從上次評論中發送最后一個時間戳，並僅在此日期向服務器詢問增量。

為此，請在您的收藏中：

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

在后端，根據from_time參數查詢數據庫。您的客戶端代碼不會更改以刷新視圖。

如果您因任何原因不想更改后端代碼，請在addAll函數中添加以下行：

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

Answer 3

Backbone.Collection.merge（[選項]）

基於@ Jeb上面的響應，我已將此行為封裝到Backbone擴展中，您可以將其復制並粘貼到.js文件中並包含在您的頁面中（包括Backbone庫本身之后）。

它為Backbone.Collection對象提供了一個名為merge的方法。 它不是完全重置現有集合（如fetch所做），而是將服務器響應與現有集合進行比較並合並它們的差異。

1. 它添加了響應中的模型，但不包含現有集合中的模型。
2. 它會刪除現有集合中的模型，但不會刪除響應中的模型。
3. 最后，它更新現有集合和響應中的模型屬性。

觸發所有預期事件以添加，刪除和更新模型。

選項哈希采用success和error回調，它們將作為參數傳遞(collection, response) ，並提供第三個回調選項，稱為complete ，無論成功或錯誤如何都會執行（主要用於輪詢方案）。

它會觸發名為“merge：success”和“merge：error”的事件。

這是擴展名：

// 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; });
};

簡單使用場景：

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

錯誤處理使用場景：

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 4

制作重復的集合。 獲取（）它。 比較兩者以找到增量。 應用它們。

      /*
       * 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; });
      },