具有模型属性的Ember计算 [英] Ember calculation with model attributes

问题描述

我想计算一个票价的总结果。您可以在这里看到： http://emberjs.jsbin.com/yudofozoqu/1/

I want to calculate the total result for a fare. You can see here: http://emberjs.jsbin.com/yudofozoqu/1/

它由价值数量组成：

{{input value=quantity}}

乘以可在选择选项中选择的具体票价：

multiplied by the specific fare which can be selected in the select option:

{{view Em.Select prompt="test" contentBinding="controllers.fare.content" optionLabelPath="content.name" optionValuePath="content.id" selectionBinding="controllers.fare.selectedFare" }}

总结果必须对应到我在我的模型中设置的总价值：

The total result has to correspond to the total value I have set up in my model:

{{input value=total}}

App.Invoice = DS.Model.extend({
  name        : DS.attr('string'),
  quantity    : DS.attr('string'),
  total       : DS.attr('string')
});

App.Invoice.FIXTURES = [
 {
   id: 1,
   quantity: null,
   total: null
 }
];

如何正确执行？

推荐答案

您需要创建一个函数来观看数量和 fare.selectedFare 属性，所以它可以计算总数。例如：

You need to create a function to watch for changes in the quantity and fare.selectedFare properties so it can calculate the total. For example:

// this should be added to the IndexController
updateTotal: function() {

  // get the reference to the values of fare and quantity
  var quantity = this.get('quantity'),
      fare = this.get('controllers.fare.selectedFare.id');

  // massage them to make sure your stuff is not gonna break
  if (isNaN(fare)) { fare = 0; }
  if (isNaN(quantity)) { quantity = 0; }

  // calculate
  var total = fare * quantity;

  // set the total
  this.set('total', total);

}.observes('quantity', 'controllers.fare.selectedFare')

确定。这样做有效，但考虑在后台保存记录（在服务器控制器中）进行总计算，并将总计属性转换为具有相同概念的计算属性的代码。根据你在做什么，如果它涉及到浮点数/十进制/异常计算，（我倾向于认为），你可以期待更多的精度与静态类型（通常在服务器上）而不是JavaScript

Ok. This works, but consider doing the total calculation in the backend as you save the record (in your server controller) and turn the total attribute into a computed property with the same general idea of the code above. Depending on what you are doing, if it involves float/decimal/exotic calculations, (I tend to think that) you can expect more accuracy with static types (generally on the server) instead of JavaScript

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