将属性添加到使用 Knockout JS 映射插件创建的视图模型

Question

我正在研究 Knockoutjs 网站上的映射插件示例。

这是示例数据。

Knockout JS 映射插件

var data = {
    name: 'Scott',
    children: [
        { id : 1, name : 'Alice' }
    ]
}

该示例展示了如何覆盖其中一个子项的映射，但如何我是否需要更改基础对象的映射？

例如，如果我想向 Scott 添加“FavouriteChild”属性，我该怎么做？

我假设我需要在基本映射上使用创建函数，但我无法在任何地方找到语法示例。

var myChildModel = function(data) {
    ko.mapping.fromJS(data, {}, this);

    this.nameLength = ko.computed(function() {
        return this.name().length;
    }, this);
}

var mapping = {
    'children': {
        create: function(options) {
            return new myChildModel(options.data);
        }
    }
}

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

编辑：从下面接受的答案中我发现这是可行的

<span data-bind='text: AdditionalProperty'>

淘汰码

var mapping = {
    create: function (options) {
        //customize at the root level.  
        var innerModel = ko.mapping.fromJS(options.data);

        innerModel.AdditionalProperty = 'Hello World';

        return innerModel;
    }
}

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

//use this as our model bindings
ko.applyBindings(viewModel);

Answer 1

您需要在映射对象本身上使用 create 方法，例如：

var mapping = {
  //customize at the root level.  
  create: function(options) {
     //first map the vm like normal
     var vm = ko.mapping.fromJS(options.data);

     //now manipulate the returned vm in any way that you like
     vm.someProperty = "test";

     vm.someComputed = ko.computed(function() {
          return vm.first() + " " + vm.last();
     });

     //return our vm that has been mapped and tweaked
     return vm;
  }
};

Answer 2

这是基于 RP Niemeyer 解决方案的答案的延续

这里的答案基于上面的解决方案和来自他的博客 - 谢谢！我认为我应该添加一些细节，因为它解决了数组不是第一级对象的问题。

 var data = {
person: {
       children: [{ id: 1, firstName: 'Scot', lastName: 'Weise'}]
    }
};

var mapping = {
    'children': {
        create: function(options) {
            return (new (function() {
                // setup the computed binding for some reason I had
                //  to use ko.dependentObservable instead of ko.computed
                // or errors showed up.
                this.fullName = ko.dependentObservable(function() {
                    return this.firstName() + ' ' + this.lastName();
                    }, this);
                    ko.mapping.fromJS(options.data, { }, this);
                })(/* call the ctor here */));
            }
        }
    };

    // Create view model and map the data object to the model.
    var viewModel = ko.mapping.fromJS(data, {});

    // update the viewModel with the mapping object that contains 
    // some a computed property(s)
    viewModel.person = ko.mapping.fromJS(viewModel.person, mapping);
    ko.applyBindings(viewModel);

请注意，该人是第一级对象，而孩子是该人的子属性。 viewModel.person = ko.mapping.fromJS(viewModel.person, mapping) 这行一开始对我来说并不直观。

这里有一个细微的变化

person 对象是一个可观察对象，在最初从服务器 json 数据创建后添加或更新。

var viewModel = {};
$(document).ready(function () {
    var person = getPerson();

    // selected person is added to the viewModel
    viewModel.selectedPerson = ko.observable(person);
    ko.applyBindings(viewModel);
});

function getPerson() { 
// you would probably pass this into the function as a parameter. 
var person =
    {
        name: 'jim',
        children: [{ id: 1, firstName: 'jane', lastName: 'bob'}]
    };

    var mapping = {
        'children': {
            create: function (options) {
                return (new (function () {
                    // setup the computed binding
                    this.fullName = ko.dependentObservable(function () {
                    return this.firstName() + ' ' + this.lastName();
                    }, this);
                    ko.mapping.fromJS(options.data, {}, this);
                })(/* call the ctor here */));
            }
        }
    };

    var result = ko.mapping.fromJS(person, mapping);
    return result;
}

html 中的一些绑定代码

最终，您需要在某些时候使用它，如下所示：

<div data-bind="foreach:viewModel.selectedPerson().children">
    <span data-bind="text:fullName"></span>
</div>

感谢您的帮助！如果没有你的博文，我不可能走到这一步。

Answer 3

请注意，要在子对象上定义额外的计算可观察量，您将需要传递另一组映射选项

var mapping = {
  create: function(options) {
    //customize at the root level.  

    var mapping2 = {
      'children': {
        create: function(options) {
          //customize children also

        }
      }
    }

    //call ko.mapping.fromJS on the options.data as well with further customization
    ko.mapping.fromJS(options.data, mapping2, this);
  }
};

Answer 4

另一个例子基于 Jason 和 RP Niemeyer 提供的示例。

data 是我们在 ajax 查询后得到的结果，我们在其上添加两个嵌套的可观察对象（viewModel.weekly.selectedWeek 和 viewModel.monthly.selectedMonth ）：

    var data = {
        "date": "2017-03-28",
        "weekly": {
            "weeks": [
                {
                    "id": "201701",
                    "label": "Week 1"
                },
                {
                    "id": "201702",
                    "label": "Week 2"
                }
            ]
        },
        "monthly": {
            "months": [
                {
                    "id": "201701",
                    "label": "01/2017"
                },
                {
                    "id": "201702",
                    "label": "02/2017"
                }
            ]
        }
    }

    var viewModelMapping = {
        create: function (options) {
            return (new (function () {
                // viewModel root level
                var mapping2 = {
                    'weekly': {
                        create: function (options) {
                            // viewModel.weekly
                            return new function () {
                                var model = ko.mapping.fromJS(options.data, {}, this);
                                model.selectedWeek = ko.observable();
                                return model;
                            };
                        }
                    },
                    'monthly': {
                        create: function (options) {
                            // viewModel.monthly
                            return new function () {
                                var model = ko.mapping.fromJS(options.data, {}, this);
                                model.selectedMonth = ko.observable();
                                return model;
                            };
                        }
                    }
                };

                ko.mapping.fromJS(options.data, mapping2, this);
            })());
        }
    };


    var viewModel = ko.mapping.fromJS(data, viewModelMapping);
    ko.applyBindings(viewModel);