backbone模型层浅析
Model层有两个类： Model, Collection
1.Model
不翻文档，我们用代码说话。
首先分析下类。
var myM = Backbone.Model.extend({})//构造一个Model类，myM
这个类居然是空的，没有官方所说的那么多属性啊，难道underscore失灵了？
>_.keys(myM) ["extend", "__super__"] >_.keys(Backbone.Model) ["extend"]
默认情况下，子类比父类多了一个__super__的东东，这到底是啥？
>_.isObject(myM.__super__) true
对象。 在观察下：
>_.keys(myM.__super__) ["on", "once", "off", "trigger", "stopListening", "listenTo", "listenToOnce", "bind", "unbind", "changed", "validationError", "idAttribute", "initialize", "toJSON", "sync", "get", "escape", "has", "set", "unset", "clear", "hasChanged", "changedAttributes", "previous", "previousAttributes", "fetch", "save", "destroy", "url", "parse", "clone", "isNew", "isValid", "_validate", "keys", "values", "pairs", "invert", "pick", "omit"]
结论：父类的指针？ 官方文档中列举的接口（函数/事件/属性）出现了，如上。
比较关心数据的同步，看看fetch的实现：
function (options) {
options = options ? _.clone(options) : {};
if (options.parse === void 0) options.parse = true;
var model = this;
var success = options.success;
options.success = function(resp) {
if (!model.set(model.parse(resp, options), options)) return false;
if (success) success(model, resp, options);
model.trigger('sync', model, resp, options);
};
wrapError(this, options);
return this.sync('read', this, options);
}
可以看出，可以有success回调，myM.fetch({success:function(model,response,options){}); 即成功的回调函数接受三个参数。
其次是fetch会调用本身的sync函数(最后一行)。
function () {
return Backbone.sync.apply(this, arguments);
}
云里雾里。过。
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分析类的实例。
构造一个myM类的实例并分析：
>m_obj= new myM;
s {cid: "c6", attributes: Object, _changing: false, _previousAttributes: Object, changed: Object…}
>_.isObject(m_obj)
true
>_.keys(m_obj)
["cid", "attributes", "_changing", "_previousAttributes", "changed", "_pending"]
首先可以看出，实例的属性，跟类的属性很不相同，且跟父类的属性似乎一点关系都没有（没有继承？）。
真的是这样么？
>_.functions(m_obj) ["_validate", "bind", "changedAttributes", "clear", "clone", "constructor", "destroy", "escape", "fetch", "get", "has", "hasChanged", "initialize", "invert", "isNew", "isValid", "keys", "listenTo", "listenToOnce", "off", "omit", "on", "once", "pairs", "parse", "pick", "previous", "previousAttributes", "save", "set", "stopListening", "sync", "toJSON", "trigger", "unbind", "unset", "url", "values"]
好吧，这个跟myM.__super__有一定的交集。交集为：
>m_obj_funcs = _.functions(m_obj)
base_funcs = _.functions(myM.__super__)
_.filter(base_funcs, function(f){return _.contains(m_obj_funcs,f)})
["_validate", "bind", "changedAttributes", "clear", "clone", "destroy", "escape", "fetch", "get", "has", "hasChanged", "initialize", "invert", "isNew", "isValid", "keys", "listenTo", "listenToOnce", "off", "omit", "on", "once", "pairs", "parse", "pick", "previous", "previousAttributes", "save", "set", "stopListening", "sync", "toJSON", "trigger", "unbind", "unset", "url", "values"]
m_obj又有多出来哪些函数呢？
>_.filter(m_obj_funcs, function(f){return !_.contains(base_funcs,f);})
["constructor"]
似乎是构造器
>m_obj.constructor
function (){ return parent.apply(this, arguments); }
属性
["cid", "attributes", "_changing", "_previousAttributes", "changed", "_pending"]
（提示：回到之前构造m_obj的部分看看。）
先剧透下，attributes是属性键值对集合(JSON对象)，可写（如果只要一个只读的attributes，使用对象实例的toJSON()方法）。比如，
>m_obj.set({'name':'tommy','blog':'http://www.cnblogs.com/Tommy-Yu'})
>m_obj.attributes
Object {name: "tommy", blog: "http://www.cnblogs.com/Tommy-Yu"}
其次，changed也是一个JSON对象，记录该实例哪些属性被改变了---只记录修改的部分，会被backbone分析，然后传给change事件的处理方法。如下：
>m_obj.set({'name':'joe'})
>m_obj.changed
Object {name: "joe"}
_previousAttributes,记录变更前的对象，有利于数据进行对比，和还原（比如撤销操作）。
>m_obj._previousAttributes
Object {name: "tommy", blog: "http://www.cnblogs.com/Tommy-Yu"}
至于cid这东东，一个临时的id吧。自动给某个类(比如myM)的对象按照数字顺序编号。
最后就是changing。
函数
["_validate", "bind", "changedAttributes", "clear", "clone", "destroy", "escape", "fetch", "get", "has", "hasChanged", "initialize", "invert", "isNew", "isValid", "keys", "listenTo", "listenToOnce", "off", "omit", "on", "once", "pairs", "parse", "pick", "previous", "previousAttributes", "save", "set", "stopListening", "sync", "toJSON", "trigger", "unbind", "unset", "url", "values"]
鉴于篇幅有限，介绍重点的：
initialize()--- 在对象被new出来的时候调用，可以在这里做一些初始化。
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set() ---上面已经演示过了，设置对象的attributes属性。set之前会调用_validate(attributes)方法--如果有定义---返回值为验证是否通过(true/false)。
has(attr) -- 判断对象的attributes是否具有attr属性
>m_obj.has('name')
true
>m_obj.has('age')
false
get(attr) -- 获取对象的attributes属性中的某一个key的值：
>m_obj.get('name')
"tommy"
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previousAttributes() --- _previousAttributes属性的get封装
>m_obj.previousAttributes()
Object {name: "tommy", blog: "http://www.cnblogs.com/Tommy-Yu"}
previous(key) -- 等同于 _previousAttributes[key]
>m_obj.previous('name')
"tommy"
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toJSON() -- 转化为json对象
>m_obj.toJSON()
Object {name: "tommy", blog: "http://www.cnblogs.com/Tommy-Yu"}
keys() -- 将键转化为数组
>m_obj.keys() ["name", "blog"]
values() -- 将值转化为数组
m_obj.values() ["tommy", "http://www.cnblogs.com/Tommy-Yu"]
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isNew() -- 是否客户端新建对象（与服务器同步时用到）
>m_obj.isNew() true
isValide()-- 对象是否通过了验证
会调用_validate(attributes)。attributes是键值对集合。
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bind(时间代码， 时间处理函数)
事件代码有：change, error, sync, ....
分别对应不同的处理函数，可以为匿名函数。
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CRUD操作： fetch/save/destroy
比较一般的：sync
前提：配置url（string/funciton --> ajax路径）
fetch/save/destroy/sync 委托到Backbone.sync函数，此函数为Backbone与服务器通讯的核心，Backbone.sync代码如下：
function (method, model, options) {
var type = methodMap[method];
// Default options, unless specified.
_.defaults(options || (options = {}), {
emulateHTTP: Backbone.emulateHTTP,
emulateJSON: Backbone.emulateJSON
});
// Default JSON-request options.
var params = {type: type, dataType: 'json'};
// Ensure that we have a URL.
if (!options.url) {
params.url = _.result(model, 'url') || urlError();
}
// Ensure that we have the appropriate request data.
if (options.data == null && model && (method === 'create' || method === 'update' || method === 'patch')) {
params.contentType = 'application/json';
params.data = JSON.stringify(options.attrs || model.toJSON(options));
}
// For older servers, emulate JSON by encoding the request into an HTML-form.
if (options.emulateJSON) {
params.contentType = 'application/x-www-form-urlencoded';
params.data = params.data ? {model: params.data} : {};
}
// For older servers, emulate HTTP by mimicking the HTTP method with `_method`
// And an `X-HTTP-Method-Override` header.
if (options.emulateHTTP && (type === 'PUT' || type === 'DELETE' || type === 'PATCH')) {
params.type = 'POST';
if (options.emulateJSON) params.data._method = type;
var beforeSend = options.beforeSend;
options.beforeSend = function(xhr) {
xhr.setRequestHeader('X-HTTP-Method-Override', type);
if (beforeSend) return beforeSend.apply(this, arguments);
};
}
// Don't process data on a non-GET request.
if (params.type !== 'GET' && !options.emulateJSON) {
params.processData = false;
}
// If we're sending a `PATCH` request, and we're in an old Internet Explorer
// that still has ActiveX enabled by default, override jQuery to use that
// for XHR instead. Remove this line when jQuery supports `PATCH` on IE8.
if (params.type === 'PATCH' && noXhrPatch) {
params.xhr = function() {
return new ActiveXObject("Microsoft.XMLHTTP");
};
}
// Make the request, allowing the user to override any Ajax options.
var xhr = options.xhr = Backbone.ajax(_.extend(params, options));
model.trigger('request', model, xhr, options);
return xhr;
}
其主要是调用Backbone.ajax来实现数据的交互，并返回jqXHR( jquery XmlHttpResponse)。
挑选一个，比如save来看看是如何调用Backbone.sync的，save代码如下：
function (key, val, options) {
var attrs, method, xhr, attributes = this.attributes;
// Handle both `"key", value` and `{key: value}` -style arguments.
if (key == null || typeof key === 'object') {
attrs = key;
options = val;
} else {
(attrs = {})[key] = val;//attrs => Object {key: val}
}
options = _.extend({validate: true}, options);
// If we're not waiting and attributes exist, save acts as
// `set(attr).save(null, opts)` with validation. Otherwise, check if
// the model will be valid when the attributes, if any, are set.
if (attrs && !options.wait) {
if (!this.set(attrs, options)) return false;
} else {
if (!this._validate(attrs, options)) return false;
}
// Set temporary attributes if `{wait: true}`.
if (attrs && options.wait) {
this.attributes = _.extend({}, attributes, attrs);
}
// After a successful server-side save, the client is (optionally)
// updated with the server-side state.
if (options.parse === void 0) options.parse = true;
var model = this;
var success = options.success;
options.success = function(resp) {
// Ensure attributes are restored during synchronous saves.
model.attributes = attributes;
var serverAttrs = model.parse(resp, options);
if (options.wait) serverAttrs = _.extend(attrs || {}, serverAttrs);
if (_.isObject(serverAttrs) && !model.set(serverAttrs, options)) {
return false;
}
if (success) success(model, resp, options);
model.trigger('sync', model, resp, options);
};
wrapError(this, options);
method = this.isNew() ? 'create' : (options.patch ? 'patch' : 'update');
if (method === 'patch') options.attrs = attrs;
xhr = this.sync(method, this, options);
// Restore attributes.
if (attrs && options.wait) this.attributes = attributes;
return xhr;
}
注意到书第四句：
xhr = this.sync(method, this, options);
就这样，save将工作丢给了sync，其主要工作是加工options和method和设置回调以及丢给sync之前的数据验证。
以上抓到几个有用的信息点：
1. 可以在options里面传入url，它的优先级比Model里面的url要高。
2. 可以重写Model的sync，来观察model到底对这些输入参数做了什么。
3. 可以在options里面设置success回调。dataType默认是json。
4. options里面的其他选项：
- url , 优先级比Backbone.Model.url要高
- data , 如果没设置，则 contenttype有可能为'application/json'
- attrs , data的候补
- emulateJSON , 兼容旧的server，JSON-> HTML Form , ContentType为'application/x-www-form-urlencoded', data为空
- emulateHTTP , 此选项用于兼容更旧的server， 在http头里面加入 X-HTTP-Method-Override等
- wait , 是否调用_validate函数
- parse, 函数/void 0, 客户端解析server传回的数据的函数，默认实现为：
function (resp, options) { return resp; } - success, 成功回调 function(model, reponse, options)
- patch ,??
fetch的调用链
fetch -> this.sync -> Backbone.sync -> success(model, reponse, options) -> this.parse -> this.set -> this._validate -> changed -> update view
由于篇幅关系，代码就不在这里上了。简单来说，就是fetch，如果顺利的话，直接改变了视图。
转载请注明本文来自Tommy.Yu的博客，谢谢！
