DataWeave合并JSON时无法移除嵌套对象中null值的问题

问题场景 #

需要合并payload与patch两个JSON对象，规则如下：

• 用patch的字段值覆盖payload对应字段（空字符串等非null值正常保留）
• 若patch中某字段值为null，则移除payload中对应的该字段
• 嵌套对象需遵循同样规则

但现有代码仅能处理顶层字段的null移除，嵌套对象location-1中的pin字段（patch中设为null）无法被移除，不符合预期输出。

输入Payload #

{ 
 "firstname":"John",
 "lastname":"Sam",
 "city": "San Jose",
 "path": "additional",
 "location-1": {
   "address": "USA",
   "pin": null
  },
  "location-2": {
   "address": null,
   "place": "abc",
   "pin": null
  }
}

现有DataWeave代码 #

%dw 2.0
output application/json 
import mergeWith from dw::core::Objects

var patch = {
    lastname:"Courtney",
    age:"18",
    path: "",
    company: "MR",
    firstname: null,
    city: null,
  "location-1": {
    "address": "USA",
    "pin": null
    }
  }
---
(payload mergeWith ((patch)) filterObject ($ != null ))

预期输出 #

{  
  "lastname": "Courtney",
  "age": "18",
  "path": "",
  "company": "MR",
  "location-1": {
    "address": "USA"
   },
   "location-2": {
    "address": null,
    "place": "abc",
    "pin": null
  }
}

问题原因 #

filterObject ($ != null)仅作用于顶层键值对，嵌套对象本身不属于null，会被完整保留，其内部的null字段不会被过滤。同时要注意：我们只需要移除patch中明确设置为null的字段，payload原生的null字段（如location-2内的字段）需保留，不能全局过滤所有null。

解决方案 #

自定义递归合并函数，处理对象的嵌套层级，精准移除patch中设为null的字段：

%dw 2.0
output application/json

// 递归合并并移除patch中指定为null的字段
fun mergeAndCleanNull(payload: Any, patch: Any): Any = 
    if (payload is Object and patch is Object)
        patch reduce ((patchVal, patchKey) -> 
            if (patchVal == null)
                // patch字段为null，移除payload对应字段
                payload - patchKey
            else
                // 递归处理嵌套对象，非对象类型直接覆盖
                payload ++ { (patchKey): mergeAndCleanNull(payload[patchKey] default {}, patchVal) }
        )
    else if (patch != null)
        // 非对象类型，patch值非null则覆盖
        patch
    else
        // patch值为null，保留原payload内容
        payload

var patch = {
    lastname:"Courtney",
    age:"18",
    path: "",
    company: "MR",
    firstname: null,
    city: null,
    "location-1": {
        "address": "USA",
        "pin": null
    }
}
---
mergeAndCleanNull(payload, patch)

函数逻辑说明 #

1. 递归判断对象类型：若payload和patch均为对象，遍历patch的每个键值对
2. 若patch字段值为null，直接从payload中移除对应键
3. 若patch字段值为对象，递归调用函数处理嵌套层级的合并与null移除
4. 非对象类型（字符串、数字等）：若patch值非null则覆盖payload，否则保留原内容

运行该代码后，会精准移除所有patch中设为null的字段（包括顶层的firstname、city，以及嵌套的location-1.pin），同时保留payload原生的null字段。

内容的提问来源于stack exchange，提问作者anonymous