如何用JSLT遍历JSON数组并计算duration字段？

问题背景 #

现有如下JSON数据：

{
  "id": "12345",
  "date_open": "2021-09-09",
  "date_last_updated": "2021-09-21",
  "status": "open",
  "project_name": "Project:5",
  "office": [
    {
      "name": "office_one",
      "completed": true,
      "required": true,
      "contact_date": "2021-09-13",
      "response_date": "2021-09-15",
      "completion_date": "2021-09-15"
    },
    {
      "name": "office_two",
      "completed": true,
      "required": true,
      "contact_date": "2021-09-13",
      "response_date": "2021-09-21",
      "completion_date": "2021-09-21"
    },
    {
      "name": "office_three",
      "completed": false,
      "required": false,
      "contact_date": null,
      "response_date": null,
      "completion_date": null
    },
    {
      "name": "office_four",
      "completed": false,
      "required": true,
      "contact_date": "2021-08-23",
      "response_date": "2021-09-01",
      "completion_date": null
    }
  ]
}

已实现days_open字段的计算逻辑：

let date_started = parse-time(.date_open, "yyyy-MM-dd")
let date_last_update = parse-time(.date_last_updated, "yyyy-MM-dd")
let days_open = ($date_last_update - $date_started) / 86400

{  
  "days_open" : $days_open,
  * : .
}

现在需要遍历office数组，为每个元素按以下规则添加duration字段：

• 当required为true时：
  1. 若completion_date不为null，计算contact_date与completion_date的天数差
  2. 若completion_date为null，计算contact_date与response_date的天数差
  3. 若response_date也为null，计算contact_date与父对象date_last_updated的天数差
• 当required为false时，duration设为null

实现方案 #

JSLT中遍历数组使用map函数，结合if-then-else条件判断即可实现需求。完整表达式如下：

let date_started = parse-time(.date_open, "yyyy-MM-dd")
let date_last_update = parse-time(.date_last_updated, "yyyy-MM-dd")
let days_open = ($date_last_update - $date_started) / 86400

{  
  "days_open" : $days_open,
  "office": map(.office, function($item) {
    // 解析当前office项的contact_date（若存在）
    let contact_time = if ($item.contact_date) then parse-time($item.contact_date, "yyyy-MM-dd") else null
    // 根据规则确定结束时间
    let end_time = 
      if ($item.completion_date) then parse-time($item.completion_date, "yyyy-MM-dd")
      else if ($item.response_date) then parse-time($item.response_date, "yyyy-MM-dd")
      else $date_last_update
    // 计算duration
    let duration = 
      if ($item.required and $item.contact_date) then ($end_time - $contact_time) / 86400
      else null
    
    // 返回原字段+新增的duration
    {
      "duration": $duration,
      *: $item
    }
  }),
  // 保留原对象其他字段
  * : . - "office"
}

代码说明 #

1. 变量复用：提前解析父对象的date_last_update，避免在数组遍历中重复解析，提升效率
2. 数组遍历：使用map(.office, function($item) { ... })遍历office数组，对每个元素$item进行处理
3. 条件判断：按优先级依次判断completion_date、response_date，最后 fallback到父对象的date_last_update作为结束时间
4. duration计算：仅当required为true且contact_date不为空时计算天数差，否则设为null
5. 字段保留：使用*: $item保留原office元素的所有字段，再新增duration；父对象部分用* : . - "office"保留除office外的原字段，避免重复输出

输出结果 #

执行上述表达式后，将得到符合要求的JSON结构：

{
  "id": "12345",
  "date_open": "2021-09-09",
  "date_last_updated": "2021-09-21",
  "days_open": 12,
  "status": "open",
  "project_name": "Project:5",
  "office": [
    {
      "name": "office_one",
      "completed": true,
      "required": true,
      "contact_date": "2021-09-13",
      "response_date": "2021-09-15",
      "completion_date": "2021-09-15",
      "duration": 2
    },
    {
      "name": "office_two",
      "completed": true,
      "required": true,
      "contact_date": "2021-09-13",
      "response_date": "2021-09-21",
      "completion_date": "2021-09-21",
      "duration": 8
    },
    {
      "name": "office_three",
      "completed": false,
      "required": false,
      "contact_date": null,
      "response_date": null,
      "completion_date": null,
      "duration": null
    },
    {
      "name": "office_four",
      "completed": false,
      "required": true,
      "contact_date": "2021-08-23",
      "response_date": "2021-09-01",
      "completion_date": null,
      "duration": 9
    }
  ]
}

内容的提问来源于stack exchange，提问作者user20409421