Azure Logic Apps中Compose与If块验证JSON属性存在性问题

需求背景 #

需要从以下JSON数据中提取email、first name、last name字段，组合成新的JSON对象：

{
  "email": "donald.duck@waltdisney.com",
  "phone number": "+123 321 111 333",
  "fields": [
    {
      "description": "name",
      "value": "Mickey",
      "id": 1
    },
    {
      "description": "first name",
      "value": "Donald",
      "id": 1
    },
    {
      "description": "last name",
      "value": "Duck",
      "id": 3
    },
    {
      "description": "age",
      "value": "1",
      "id": 4
    }
  ]
}

当前采用foreach遍历fields数组，结合Compose和If块实现，但条件判断结果始终不符合预期。

问题代码展示 #

// this works correctly:
"Compose": {
    "inputs": {
        "@{item()['description']}": "@{item()['value']}"
    },
    "runAfter": {},
    "type": "Compose"
},
"condition": {
    "actions": {
// this works correctly
        "set_variable": {
            "inputs": {
                "name": "Result-fields",
                "value": "@outputs('Union_Compose')"
            },
            "runAfter": {
                "Union_Compose": [
                    "Succeeded"
                ]
            },
            "type": "SetVariable"
        },
// this works correctly
        "Union_Compose": {
            "inputs": {
                "result": "@{union(variables('Result-fields'), outputs('Compose'))}"
            },
            "runAfter": {},
            "type": "Compose"
        }
    },
// I tried different conditions:
// body('Compose') contains "first name" or "last name": result: everytime false
// body('Compose')['first name'] or body('Compose')['last name'] not equals null result: everytime true
// body('Compose')['first name'] or body('Compose')['last name'] equals "*" (as wild card) but the result is everytime false!
    "expression": {
        "or": [
            {
                "contains": [
                    "@{body('Compose')}",
                    "first name"
                ]
            },
            {
                "contains": [
                    "@{body('Compose')}",
                    "last name"
                ]
            }
        ]
    },
    "runAfter": {
        "Compose": [
            "Succeeded"
        ]
    },
    "type": "If"
}

条件判断失效原因分析 #

1. contains(body('Compose'), "first name") 始终为false
   body('Compose')返回的是JSON对象（如{"name": "Mickey"}），但contains函数仅支持检查字符串子串或数组元素，直接传入对象无法识别键名，导致判断失效。

2. body('Compose')['first name'] or body('Compose')['last name'] not equals null 始终为true
   遍历非目标字段时，访问不存在的键会返回null，但表达式未正确使用Logic Apps的逻辑函数，直接拼接的逻辑或被解析为非空值，导致判断始终为true。

3. 通配符*判断失效
   Logic Apps的equals函数不支持通配符匹配，equals(body('Compose')['first name'], "*")会严格匹配字符串*，而非作为通配符使用，因此结果始终为false。

解决方案 #

方案1：修正条件表达式（基于遍历项直接判断） #

无需依赖Compose输出，直接检查当前遍历项的description字段：

"expression": {
    "or": [
        {
            "equals": [
                "@{item()['description']}",
                "first name"
            ]
        },
        {
            "equals": [
                "@{item()['description']}",
                "last name"
            ]
        }
    ]
}

或用contains简化逻辑：

"expression": {
    "contains": [
        ["first name", "last name"],
        "@{item()['description']}"
    ]
}

方案2：简化流程（无需foreach和变量） #

用reduce和union函数一次性构建目标JSON，避免遍历和条件判断的复杂度：

@{
    union(
        createObject('email', body('原始JSON')['email']),
        reduce(
            body('原始JSON')['fields'],
            createObject(),
            if(
                contains(['first name','last name'], item()['description']),
                union(item(), createObject(item()['description'], item()['value'])),
                item()
            )
        )
    )
}

执行后直接生成目标JSON：

{
  "email": "donald.duck@waltdisney.com",
  "first name": "Donald",
  "last name": "Duck"
}

内容的提问来源于stack exchange，提问作者Filippo1980