在Thymeleaf中创建空的数据属性 [英] Creating empty data-attributes in Thymeleaf

问题描述

我试图在Thymeleaf 3.0.3（春季4.3.7）中创建一个具有自定义数据属性的元素：

I'm attempting to create an element in Thymeleaf 3.0.3 (Spring 4.3.7) with a custom data-attribute:

<input th:attr="data-customAttr=${item.getMyAttr()}" />

如果item.getMyAttr（）的结果是'someVal'，则呈​​现的HTML会输出到是：

If the result of item.getMyAttr() was 'someVal', then the rendered HTML comes out to be:

<input data-customAttr='someVal' />

但是，如果item.getMyAttr（）的结果为空字符串，则会抛出自定义属性完全由Thymeleaf淘汰。呈现的HTML看起来像：

However, if the result of item.getMyAttr() is an empty string, the custom attribute is thrown out by Thymeleaf altogether. The rendered HTML looks like:

<input />

我需要知道自定义属性是否已定义，为空，缺失或未定义。根据此讨论：空的HTML5数据属性是否有效？
，空的数据属性应该是完全有效的。

I need to know whether the custom attribute was defined and empty or missing and undefined. According to this discussion: Are empty HTML5 data attributes valid? , empty data-attributes should be perfectly valid.

经过一番挖掘之后，我遇到了以下测试用例，似乎表明Thymeleaf可以不会渲染空的数据属性，这就是为什么它在渲染之前将其丢弃。以下Thymeleaf代码段呈现得很好：

After a little digging I ran into the following test case that seems to show Thymeleaf can't render empty data-attributes, which is why it's throwing them out before render-time. The following Thymeleaf snippet renders just fine:

<input th:attr="__${'data-customAttr=' + 'someVal'}__" />

虽然两者都引发错误：

<!-- Throws: 'org.thymeleaf.exceptions.TemplateProcessingException: Could not parse as assignation sequence' -->
<input th:attr="__${'data-customAttr=' + ''}__" />
<input th:attr="__${'data-customAttr'}__" />

这是Thymeleaf中的错误吗？任何帮助将不胜感激。我也很高兴提供其他任何相关信息。

Is this a bug in Thymeleaf? Any help would be greatly appreciated. I'm happy to provide any other relevant information as well.

编辑：这是我在相当大的应用程序中经常使用的一项功能。虽然我知道有几种解决方法，但它们都使我完成一个非常简单的任务所需编写/维护的代码量增加了。我希望有一个长期解决方案，即使该解决方案是这是一个错误，请报告。

This is a feature I'm making heavy use of in a fairly large application. While I'm aware that there are several workarounds, they all compound the amount of code I have to write/maintain just to accomplish a very simple task. I'm hoping for a long-term solution, even if that solution is "This is a bug, please report it".

推荐答案

__ 语法没有什么特别的……只是使它两次运行评估程序。之所以不起作用，是因为在每种情况下，它都会解析为无效的百里香叶表达。

The __ syntax isn't anything special... it just makes it run the evaluator twice. The reason it doesn't work is because in each case, it resolves to an invalid thymeleaf expression.

例如：

<input th:attr="__${'data-customAttr=' + ''}__" />
<!-- evaluates to -->
<input th:attr="data-customAttr=" />
<!-- which is an invalid expression -->

与

<input th:attr="__${'data-customAttr'}__" />
<!-- evaluates to -->
<input th:attr="data-customAttr" />
<!-- which is again, an invalid expression -->

百里香叶确实不会添加空属性。因此，我认为您要做的最好的事情是这样的：

It does appear that thymeleaf won't add empty attributes. So I think the best you are going to do is something like this:

<input th:attr="data-customAttr-exists=${item.getMyAttr() != null}, data-customAttr=${item.getMyAttr()}" />

然后您必须检查第一个属性以了解其是否存在，第二个值的属性。这应该可以让您了解所有情况。

And you'll have to check the first property to know whether or not it exists, and the second property for the value. This should allow you to know all cases.

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