数据绑定到Polymer中的动态路径 [英] Data binding to a dynamic path in Polymer

问题描述

我正在使用Polymer 1.0和Firebase构建一个Web应用程序，并且我希望在将数据输入到路径中且路径中带有用户ID的情况下更改视图.为此，我想做这样的事情:

I am building a web app with Polymer 1.0 and Firebase, and I want to have the view change when data was entered into a path with a user ID in the path. To do that, I want to do something like this:

[[question.answers.(user.uid).choice]]

让我详细解释.所以，在模板中，我有这样的东西:

Let me explain in more detail. So, in the template, I have something like this:

 <ul id="question-list">
    <template is="dom-repeat" items="[[questions]]" sort="_computeSort" as="question">
      <li class="card question" data-key="[[question.$key]]" question="[[question]]">
        <h3 class="content">[[question.question]]</h3>
        <p hidden$="[[ MY DATA BINDING HERE ]]">[[question.afterMessage]]</p>
      </li>
    </template>
  </ul>

如果您查看上面的<p>元素，则在hidden属性内是我希望进行数据绑定的地方. questions路径的结构如下:

If you look at the <p> element above, inside the hidden attribute is where I want to have my data binding to happen. The structure of a questions path is like this:

所以questions是问题的集合，每个问题都有一个属性afterMessage，我想在回答问题后向用户显示该属性.

So questions is a collection of questions, and each question has a property afterMessage, which I want to show the user after answering the question.

为了检查用户是否回答了问题，我在questions路径中有一个名为answers的路径.在该answers路径内，我将用户的密钥作为用户选择的密钥.

In order to check if the user has answered the question, I have a path called answers within the questions path. Inside that answers path, I have the users's key as a key to the choice that the user chose.

因此，如果用户密钥为ZjHDMDa270Uyp6sAL02Mam2ftGf2的用户登录到我的应用程序，则该用户答案的​​数据绑定路径为:

So, if a user with user key of ZjHDMDa270Uyp6sAL02Mam2ftGf2 is logged into my app, the data binding path to that user's answer would be:

[[quesion.answers.ZjHDMDa270Uyp6sAL02Mam2ftGf2.choice]]

现在上面的表达式是我要绑定的内容，但是用户ID随用户的不同而变化，那么我该怎么做呢?换句话说，我想做这样的事情:

Now this above expression is what I want to bind to, but of course the user ID changes from user to user, so how can I do this? In other words, I want to do something like this:

[[question.answers.(user.uid).choice]]

推荐答案

聚合物数据绑定不支持嵌套或表达式.您可能必须使用计算的绑定像这样:

Polymer data bindings don't support nesting or expressions. You would likely have to use a computed binding like this:

// template's computed binding
[[_getChoice(question, user.uid)]]

// script
Polymer({
  _getChoice: function(question, uid) {
    return question.answers[uid].choice;
  },
  ...
});

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