How to change value of a variable in thymeleaf?

Question

I am new to thymeleaf. I am bit confused now. Please check out the codes below

  <th:block th:with="${someVarible=false}">
    <th:block th:each="dem : ${demo}">
       <th:block th:if="${dem.status==0}">
             //Here I need to change the value of someVarible to true
       </th:block>
    </th:block>
    <th:block th:if="${someVariable}">Its true</th:block>
  </th:block>

I need to edit the value of someVarible . How can I do it. Thanks in advance.

Answer 1

You can't achieve your desired functionality as you described with Thymeleaf.

th:with does just local variable definition which is only available for evaluation inside that fragment.

<div class="example1" th:with="foo=${bar}">
    <!--/* foo is availabile here */-->
    <th:block th:text="${foo}" />
</div>
<div class="example2">
    <!--/* foo is NOT availabile here! */-->
</div>

And you can't change that variable in template. Thymeleaf is just presentation layer, you're trying to achieve something which has to be done on application layer (Java code).

On application layer (Java code) you could do:

Map<Integer, Boolean> fooMap = new HashMap<Integer, Boolean>();

for(Demo demo : demos) {
    if(demo.getStatus() == 0) {
        fooMap.put(demo.getId(), true);
    } else {
        fooMap.put(demo.getId(), false);
    }
}

And then on presentation layer (Thymeleaf):

<th:block th:each="demo : ${demos}">
    <th:block th:text="${demo.getId()}" />
</th:block>
<th:block th:each="demo : ${demos}">
    <th:block th:if="${fooMap.get(demo.getId()) == true}">It's true</th:block>
</th:block>

If you don't want to use HashMap you could use inheritance and extend object Demo.

(Please note that code which I wrote is not tested, so it may need some small fixed, but I hope that I helped you.)

Answer 2

As Lukas said, it's not possible to change the value of a variable in Thymeleaf, because that only applies to the content within that element. However it is possibe to achieve something very similar using Thymeleaf only.

You can use Collection Selection and the ^[...] syntax to select the first element in your list that matches the criteria status==0. This expression would look like:

${demo.^[status==0]}

If the demo list contains an element with status==0, then that will be returned. Otherwise, it will result in null. This can be used directly in your th:if:

<th:block th:if="${demo.^[status==0]}">Its true</th:block>

Or, if you need to use someVariable for other things too, you can assign it to a variable using th:with (Docs):

<th:block th:with="someVariable=${demo.^[status==0]}">
    <th:block th:if="${someVariable}">Its true</th:block>
</th:block>