我是否过度使用Knockout映射插件总是用它来做我的viewmodel？

Question

我还在学习Knockout的正确使用方法,并且我发现自己ko.observable在设置我的viewmodel时很快就远离了键入,而只是定义了一个对象文字,并通过映射插件传递给它

var viewModel = ko.mapping.fromJS(data);

或者至少,将所有数据填充到viewModel上的属性中,就像这样

var viewModel = { 
    ... events etc ... , 
    "data": ko.mapping.fromJS(data)
}

说实话,我一直这样做的主要原因是为了解决必须打字ko.observable和ko.observableArray重复的问题.我只是想弄清楚这是否是一个好方法,如果有任何缺点,将var x = ko.observable()所有特定声明放在一起.此外,我正在加载所有这些,而不是响应任何ajax调用等,从我可以看出,这是映射插件的设计目的.

在使用knockout的工作中,你是否仍然手动逐个声明observable,或者你使用了我使用的mapping.fromJS方法？像这样经常使用映射插件有什么特别的缺点吗？

编辑:

具体例子

在本文中,Steve通过这样做来设置他的viewModel

var initialData = [ { ... } , { ... } ]; // json from the serializer
var viewModel = {
    gifts : ko.observableArray(initialData)
};

通常,我也只是ko.mapping.fromJS用于这种情况,特别是为了确保数组中的对象也被转换为可观察对象.看看他做了什么,我的做法似乎有些过度,并增加了一些不必要的开销.

Answer 1

在使用Knockout一段时间后,我注意到映射插件有一些额外的选项,可以让您对映射过程进行更精细的控制.

控制类型和生成的属性数量

有几种方法可以实现这一点,我将讨论一些,但最终结果是你最终得到了映射插件的更轻的结果,因为一切都是不可观察的.

基本上,你把你认为不会改变的一切都留作普通的属性,只能从你想要观察的特定项目中做出可观察的.

请mapping忽略某些属性

您可以通过指定诸如ignore或之类的内容使映射插件完全从最终结果中省略属性include.这两者都以相反的方式完成了同样的事情.

注意:样本来自knockout.js映射插件文档,我添加了评论

映射插件参数: include

以下代码段将省略源对象中除通过include参数传入的属性之外的所有属性.

// specify the specific properties to include as observables in the end result 
var mapping = {
    // only include these two properties
    'include': ["propertyToInclude", "alsoIncludeThis"]
}

// viewModel will now only contain the two properties listed above, 
//    and they will be observable
var viewModel = ko.mapping.fromJS(data, mapping);

映射插件参数: ignore

如果只想省略源对象中的某些属性,请使用ignore如下所示的参数.除了指定的属性外,它将从源对象中的所有属性创建可观察对象.

// specify the specific properties to omit from the result, 
//    all others will be made observable
var mapping = {
    // only ignore these two properties
    'ignore': ["propertyToIgnore", "alsoIgnoreThis"]
}

// viewModel will now omit the two properties listed above, 
//    everything else will be included and they will be an observable
var viewModel = ko.mapping.fromJS(data, mapping);

控制哪些属性是否可观察

如果你需要包含属性,但你不认为它们需要被观察(无论出于何种原因),那么映射插件可以提供帮助.

映射插件参数: copy

如果您希望映射插件只是简单地复制普通属性而不使它们可观察,请使用此参数,如下所示.

// tell the mapping plugin to handle all other properties normally, 
//    but to simply copy this property instead of making it observable
var mapping = {
    'copy': ["propertyToCopy"]
}
var viewModel = ko.mapping.fromJS(data, mapping);

获得对映射过程的完全控制

如果您希望100%控制映射过程中创建的内容,包括在对象中放置闭包和订阅的功能,那么您需要使用"创建"选项.

具有计算属性的简单结果

这是一个示例,我将数据从ajax调用映射到具有results属性的对象.我不想要任何可观察的东西,我只想要一个简单的生成属性,它将由对象上的其他简单属性组成.也许不是最引人注目的例子,但它展示了功能.

var searchMappingConfig = {
    // specific configuration for mapping the results property
    "results": {
                    // specific function to use to create the items in the results array
        "create": function (options) {
            // return a new function so we can have the proper scope/value for "this", below
            return new function () {

                // instead of mapping like we normally would: ko.mapping.fromJS(options.data, {}, this);
                // map via extend, this will just copy the properties from the returned json element to "this"
                // we'll do this for a more light weight vm since every last property will just be a plain old property instead of observable
                $.extend(this, options.data);

                // all this to add a vehicle title to each item
                this.vehicleTitle = this.Year + "<br />" + this.Make + " " + this.Model;
                }, this);
            };
        }
    }
}

订阅和关闭和映射,哦,我的

另一种情况是,如果您想在结果中使用闭包和订阅.此示例太长,无法完整地包含在内,但它适用于车辆品牌/模型层次结构.如果模型未启用,我希望取消启用给定make(父)的所有模型(子项),并且我希望通过订阅完成此操作.

// here we are specifying the way that items in the make array are created, 
//    since makes has a child array (Models), we will specify the way that 
//    items are created for that as well
var makesModelsMappingConfig = {
   // function that has the configuration for creating makes
   "create": function (options) {
      // return a new function so we can have the proper 
      //    scope/value for "this", below
      return new function () {

         // Note: we have a parent / child relationship here, makes have models. In the 
         //    UI we are selecting makes and then using that to allow the user to select 
         //    models. Because of this, there is going to be some special logic in here 
         //    so that all the child models under a given make, will automatically 
         //    unselect if the user unselects the parent make.

         // make the selected property a private variable so it can be closure'd over
         var makeIsSelected = ko.protectedComputed(false);

         // expose our property so we can bind in the UI
         this.isSelected = makeIsSelected;

         // ... misc other properties and events ...

         // now that we've described/configured how to create the makes, 
         //    describe/configure how to create the models under the makes
         ko.mapping.fromJS(options.data, {
            // specific configuration for the "Models" property                  
            "Models": {
               // function that has the configuration for creating items 
               //    under the Models property
               "create": function (model) {

                  // we'll create the isSelected as a local variable so 
                  //    that we can flip it in the subscription below, 
                  //    otherwise we wouldnt have access to flip it
                  var isSelected = ko.protectedComputed(false);

                  // subscribe to the parents "IsSelected" property so 
                  //    the models can select/unselect themselves
                  parentIsSelected.current.subscribe(function (value) {
                     // set the protected computed to the same 
                     //    value as its parent, note that this 
                     //    is just protected, not the actual value
                     isSelected(value);
                  });


                  // this object literal is what makes up each item 
                  //    in the Models observable array 
                  return {
                     // here we're returning our local variable so 
                     //    we can easily modify it in our subscription
                     "isSelected": isSelected,

                     // ... misc properties to expose 
                     //     under the item in the Model array ...

                  };
               }
            }
         }, this);
      };
   }
};

总而言之,我发现你很少需要100%的对象传递给插件,而你很少需要100%的对象可以观察到.深入了解映射配置选项并创建各种复杂和简单的对象.我们的想法是只获得您需要的一切,无论是更多还是更少.

Answer 2

我给你的建议也是另一个问题,我刚才在/sf/ask/524939341/上回答.

您使用映射插件的原因是合理的,也是我使用的插件.为什么要输入比你更多的代码？

根据我的淘汰经验(全部4个月),我发现我手动做的越少,让淘汰程序做他们的事情,我的应用程序似乎运行得越好.我的建议是先尝试最简单的方法.如果它不能满足您的需求,请查看简单方法如何做"事情"并确定必须更改以满足您的需求.