Backbone源码分析（一）
Backbone源码分析（二）
Backbone中主要的业务逻辑位于Model和Collection，上一篇介绍了Backbone中的Model，这篇文章中将主要探讨Collection的源码。
让我们先来看一下Collection的构造函数：
// Create a new **Collection**, perhaps to contain a specific type of `model`.
// If a `comparator` is specified, the Collection will maintain
// its models in sort order, as they're added and removed.
var Collection = Backbone.Collection = function(models, options) {
options || (options = {});
if (options.model) this.model = options.model;//model对象指定collection管理的Model类型
//comparator 排序使用
if (options.comparator !== void 0) this.comparator = options.comparator;
this._reset();// 重置集合
this.initialize.apply(this, arguments);//调用初始化方法
//如果参数中传递model数组，则利用models数组重置集合
if (models) this.reset(models, _.extend({silent: true}, options));
};接下来是在set, add, remove 中经常用到的splice函数：
// Splices `insert` into `array` at index `at`.
//将insert数组在at位置拼接到array中
var splice = function(array, insert, at) {
//防止at超出数组长度
at = Math.min(Math.max(at, 0), array.length);
//先创建一个空数组
var tail = Array(array.length - at);
var length = insert.length;
var i;
//将at之后的数组元素暂存到tail中
for (i = 0; i < tail.length; i++) tail[i] = array[i + at];
//用insert替换array中at之后的元素
for (i = 0; i < length; i++) array[i + at] = insert[i];
//将原at之后的array元素放到insert元素之后
for (i = 0; i < tail.length; i++) array[i + length + at] = tail[i];
};下面我们来讲解set函数，set函数是Collection中非常重要的一个函数，集增删改查与一身，处理了大量的核心业务逻辑：
// Update a collection by `set`-ing a new list of models, adding new ones,
// removing models that are no longer present, and merging models that
// already exist in the collection, as necessary. Similar to **Model#set**,
// the core operation for updating the data contained by the collection.
set: function(models, options) {
if (models == null) return;
// var setOptions = {add: true, remove: true, merge: true};
options = _.extend({}, setOptions, options);//setOptions是预设参数
// 如果models为原生对象，会利用Collection中model属性来转化成Model实例
if (options.parse && !this._isModel(models)) {
models = this.parse(models, options) || [];
}
var singular = !_.isArray(models);
models = singular ? [models] : models.slice();
// 处理at，确保at为合理的数字
var at = options.at;
if (at != null) at = +at; //转化为数字
if (at > this.length) at = this.length;
if (at < 0) at += this.length + 1;
var set = [];// set表示经过本次处理后应当存在于this.models中的model
var toAdd = [];// 本次操作增加的model数组
var toMerge = [];// 本次操后修改的model数组
var toRemove = [];// 本次操作删除掉的models
var modelMap = {};//modelMap是本次变化后的应该存在于Collection中的models的key集合
var add = options.add;
var merge = options.merge;
var remove = options.remove;
var sort = false;
//有comparator属性，没设置at，sort为true
//如果对collection做了插入的话，需要自己手动排序
var sortable = this.comparator && at == null && options.sort !== false;
//comparator 是model中的属性
var sortAttr = _.isString(this.comparator) ? this.comparator : null;
// Turn bare objects into model references, and prevent invalid models
// from being added.
var model, i;
//先过滤一遍，找出存在于collection中的和不存在于当前collection中的
for (i = 0; i < models.length; i++) {//处理add和existing
model = models[i];
// If a duplicate is found, prevent it from being added and
// optionally merge it into the existing model.
// get根据idAttribute || cid 来查找
var existing = this.get(model);
if (existing) {
if (merge && model !== existing) {
var attrs = this._isModel(model) ? model.attributes : model;
if (options.parse) attrs = existing.parse(attrs, options);//在这之前应该验证一下
// 使用当前属性替换model中已存在属性
existing.set(attrs, options);
toMerge.push(existing);
// 查看排序字段是否有更改
if (sortable && !sort) sort = existing.hasChanged(sortAttr);
}
// 将更的model id存到modelMap中
if (!modelMap[existing.cid]) {
modelMap[existing.cid] = true;
set.push(existing);
}
models[i] = existing;
// If this is a new, valid model, push it to the `toAdd` list.
} else if (add) {
// _prepareModel将原始对象转化为Model实例
model = models[i] = this._prepareModel(model, options);
if (model) {
toAdd.push(model);
// _addReference 将model加入到Collection的_byId中，并绑定model的所有事件
this._addReference(model, options);
modelMap[model.cid] = true;
set.push(model);
}
}
}
// Remove stale models.
if (remove) {
for (i = 0; i < this.length; i++) {
model = this.models[i];
// 在this.models中但不在本次set中的model，都要删除
if (!modelMap[model.cid]) toRemove.push(model);
}
//移除model,this.models、this._byId;移除model的绑定事件
if (toRemove.length) this._removeModels(toRemove, options);
}
// See if sorting is needed, update `length` and splice in new models.
var orderChanged = false;
var replace = !sortable && add && remove;
if (set.length && replace) {//如果同时有加减操作，便将models放到this.models中
//如果this.models中set的数据不一致，则认为order有变化。
orderChanged = this.length !== set.length || _.some(this.models, function(m, index) {
return m !== set[index];
});//没有启用排序，但是this.models与set不一致时，仍会触发sort事件
//处理完remove后，该删除的都删除掉；用set替换this.models
this.models.length = 0;
splice(this.models, set, 0);
this.length = this.models.length;
} else if (toAdd.length) {//如果仅仅是增加model，则将toAdd插入到指定位置去
if (sortable) sort = true;
splice(this.models, toAdd, at == null ? this.length : at);
this.length = this.models.length;
}
// Silently sort the collection if appropriate.
//这里排序一下，但不要触发事件，在下文统一处理
if (sort) this.sort({silent: true});
// Unless silenced, it's time to fire all appropriate add/sort/update events.
//collection跟新完毕后，再发送事件
// remove在上文删除时已触发
if (!options.silent) {
for (i = 0; i < toAdd.length; i++) {
if (at != null) options.index = at + i;
model = toAdd[i];
model.trigger('add', model, this, options);
}
if (sort || orderChanged) this.trigger('sort', this, options);
if (toAdd.length || toRemove.length || toMerge.length) {
options.changes = {
added: toAdd,
removed: toRemove,
merged: toMerge
};
this.trigger('update', this, options);
}
}
// Return the added (or merged) model (or models).
return singular ? models[0] : models;
},Collection中存储model的属性有两个：this.models数组和_byId键值对，所有的增删改查都需要对这两个属性进行更新。
set函数中主要做了以下几件事情：
- 将models参数处理成
Model的实例数组 - 处理options中的at参数，将其变成一个合理的数字
- 声明变量
set,toAdd,toMerge,toRemove,modelMap - 遍历models参数，找出其中应当更改或者加入到Collection中的model并添加到上文的变量中
- 从Collection的
this.models中删除不存在本次set中的model - 统一更改Collection中的
this.models数组 - 排序，但不要触发sort事件
- 统一处理事件: add、sort、update事件
像add函数内部就是利用set函数来处理的：
// Add a model, or list of models to the set. `models` may be Backbone
// Models or raw JavaScript objects to be converted to Models, or any
// combination of the two.
add: function(models, options) {//没有的会加进去，已存在的会根据options决定是否merge
return this.set(models, _.extend({merge: false}, options, addOptions));
},继add之后，另一个重要的操作就是remove，Collection中的remove逻辑由remove, _removeModels, _removeReference 三个函数完成
remove: function(models, options) {
//处理参数，models处理成数组
options = _.extend({}, options);
var singular = !_.isArray(models);
models = singular ? [models] : models.slice();
//删除掉models，并触发removed事件
var removed = this._removeModels(models, options);
//从Collection层面上触发update事件
if (!options.silent && removed.length) {
options.changes = {added: [], merged: [], removed: removed};
this.trigger('update', this, options);//触发update事件，注意options里面的change，这样可以方便很多事
}
return singular ? removed[0] : removed;//注意api的返回值和事件参数的设置
}, // Internal method called by both remove and set.
_removeModels: function(models, options) {
var removed = [];
for (var i = 0; i < models.length; i++) {
var model = this.get(models[i]);
if (!model) continue;
// 首先从this.models数组中删除model
var index = this.indexOf(model);
this.models.splice(index, 1);
this.length--;
// Remove references before triggering 'remove' event to prevent an
// infinite loop. #3693
// 从_byId中删除model的引用
delete this._byId[model.cid];
var id = this.modelId(model.attributes);
if (id != null) delete this._byId[id];
// 触发Collection的remove事件
if (!options.silent) {
options.index = index;
model.trigger('remove', model, this, options); //被删除的model也触发remove事件
}
// 删除model的引用和移除model的绑定事件
removed.push(model);
this._removeReference(model, options);
}
return removed;
}, // Internal method to sever a model's ties to a collection.
_removeReference: function(model, options) {
//断开model与collection的关联
delete this._byId[model.cid];
var id = this.modelId(model.attributes);
if (id != null) delete this._byId[id];
if (this === model.collection) delete model.collection;
// 移除所有的绑定事件
model.off('all', this._onModelEvent, this);
},remove整体逻辑如下：
- 处理models参数
- 从
this.models与_byId中删除model，触发Collection的remove事件 - 断开model与Collection的关联，移除model的绑定事件
- 触发Collection的update事件
与_removeReference对应的是_addReference，它的作用于_removeRenence相反:
// Internal method to create a model's ties to a collection.
_addReference: function(model, options) {
//将model与collection关联起来，绑定model的各种事件
this._byId[model.cid] = model;
var id = this.modelId(model.attributes);
if (id != null) this._byId[id] = model;
model.on('all', this._onModelEvent, this);
},最后要提一下的是reset函数：
// When you have more items than you want to add or remove individually,
// you can reset the entire set with a new list of models, without firing
// any granular `add` or `remove` events. Fires `reset` when finished.
// Useful for bulk operations and optimizations.
reset: function(models, options) {//reset中不会触发add和remove事件
options = options ? _.clone(options) : {};
for (var i = 0; i < this.models.length; i++) {
//断开与Collection的链接，和移除model的事件
this._removeReference(this.models[i], options);
}
options.previousModels = this.models;//多看设计
this._reset();//将Collection置空，length、this.models、this._byId
models = this.add(models, _.extend({silent: true}, options));
// 触发事件
if (!options.silent) this.trigger('reset', this, options);
return models;
},