技术问询：从JSON数组查唯一ID元素及FreeMarker按人员ID分组周

嘿，刚上手FreeMarker处理JSON数组确实容易踩坑，我来帮你搞定这两个需求！

首先假设你的JSON数据已经转成了FreeMarker能识别的序列（如果还是字符串，下面会附解析方式）。比如我们要找person_id为"1414"的员工记录，可以用?filter来筛选匹配的元素，代码示例如下：

<#-- 如果你的JSON还是字符串，先解析成序列 -->
<#assign jsonStr = '[{"Hours":"5.500","Status":"Draft","Week":"17","person_name":"Raj","person_id":"1414"}, {"Hours":"0.500","Status":"Draft","Week":"17","person_name":"Raj","person_id":"1414"}, {"Hours":"24.500","Status":"Draft","Week":"14","person_name":"Mukesh","person_id":"1046"}]'>
<#assign employeeHours = jsonStr?eval>

<#-- 筛选出所有匹配目标ID的记录 -->
<#assign targetRecords = employeeHours?filter(item -> item.person_id == "1414")>

<#if targetRecords?size > 0>
  <h4>找到ID为1414的员工记录：</h4>
  <ul>
    <#list targetRecords as record>
      <li>姓名：${record.person_name} | 周数：${record.Week} | 工时：${record.Hours} | 状态：${record.Status}</li>
    </#list>
  </ul>
<#else>
  <p>未找到对应ID的元素</p>
</#if>

如果只需要第一个匹配的元素，在targetRecords后面加?first就行，比如<#assign targetRecord = targetRecords?first>。

FreeMarker自带的?group_by内置函数刚好能解决分组问题，它会把序列按指定属性分组，生成一个键为分组值、值为对应记录列表的哈希结构。结合?unique还能给每个员工的周数去重，代码如下：

<#-- 同样先确保JSON已解析为序列（如果是字符串的话） -->
<#assign jsonStr = '[{"Hours":"5.500","Status":"Draft","Week":"17","person_name":"Raj","person_id":"1414"}, {"Hours":"0.500","Status":"Draft","Week":"17","person_name":"Raj","person_id":"1414"}, {"Hours":"24.500","Status":"Draft","Week":"14","person_name":"Mukesh","person_id":"1046"}]'>
<#assign employeeHours = jsonStr?eval>

<#-- 按person_id分组 -->
<#assign groupedByPerson = employeeHours?group_by("person_id")>

<#list groupedByPerson as personId, records>
  <h3>员工信息：ID=${personId} | 姓名=${records[0].person_name}</h3>
  
  <h4>参与的周数（去重后）：</h4>
  <#-- 提取所有Week并去重 -->
  <#assign uniqueWeeks = records?map(r -> r.Week)?unique>
  <ul>
    <#list uniqueWeeks as week>
      <li>第${week}周</li>
    </#list>
  </ul>

  <h4>所有工时记录：</h4>
  <table border="1" cellpadding="4">
    <tr>
      <th>周数</th>
      <th>工时</th>
      <th>状态</th>
    </tr>
    <#list records as record>
      <tr>
        <td>${record.Week}</td>
        <td>${record.Hours}</td>
        <td>${record.Status}</td>
      </tr>
    </#list>
  </table>
  <hr>
</#list>

这段代码会先把所有记录按person_id分组，然后对每个员工的记录提取周数并去重，最后展示该员工的所有工时明细。

内容的提问来源于stack exchange，提问作者Ghanshyam Mule