AJV中JSON Schema的if/else/then逻辑失效问题排查

用AJV做JSON Schema校验时碰上个怪事：本来要根据propertyType的值，给目标对象的键套不同的正则规则——propertyType是"123"时，键不能有空格；是其他值时，允许带空格。但测下来不管propertyType是不是"123"，都只走then里的规则，else完全没生效。

原Schema片段：

"properties": {
  "location": {
    "title": "Path",
    "type": "string",
    "description": "The relative JSON path of the location to which the properties should be set",
    "examples": ["abc", "def"],
    "pattern": "^.*$"
  },
  "properties": {
    "title": "Properties",
    "type": "object",
    "description": "The set of properties that shall be set on the given relative path",
    "if": {
      "properties": {
        "propertyType": {
          "const": "123"
        }
      }
    },
    "then": {
      "patternProperties": {
        "^[-&/_.:a-zA-Z0-9]+$": {
          "anyOf": [{
              "type": "string"
            },
            {
              "type": "number"
            },
            {
              "type": "boolean"
            }
          ]
        }
      },
      "additionalProperties": false
    },
    "else": {
      "patternProperties": {
        "^.*$": {
          "anyOf": [{
              "type": "string"
            },
            {
              "type": "number"
            },
            {
              "type": "boolean"
            }
          ]
        }
      },
      "additionalProperties": false
    }
  }
}

测试数据1（符合预期，校验失败）：

{
  "type" : "xyz",
  "anchor" : {
    "propertyType": "123"
  },
  "setProperties" : {
    "random_123 " : "value1"
  }
}

测试数据2（不符合预期，还是按then规则校验失败）：

{
  "type" : "xyz",
  "anchor" : {
    "propertyType": "456"
  },
  "setProperties" : {
    "random_123 " : "value1"
  }
}

两个关键错误：

• if规则找错地方了：原Schema里把if写在要校验的properties对象内部，它只会检查这个对象自己有没有propertyType属性，但实际propertyType在顶层的anchor对象里，和setProperties是平级的。而且原if没加required，只要对象里没propertyType，这个条件就会判定为“通过”，自然每次都走then规则。
• Schema键名和测试数据对不上：Schema里要校验的对象键是properties，但测试数据里对应的是setProperties，等于Schema没盯对目标，规则白写。

{
  "type": "object",
  "properties": {
    "type": { "type": "string" },
    "anchor": {
      "type": "object",
      "properties": {
        "propertyType": { "type": "string" }
      },
      "required": ["propertyType"]
    },
    "setProperties": {
      "title": "Properties",
      "type": "object",
      "description": "The set of properties that shall be set on the given relative path"
    }
  },
  "required": ["anchor", "setProperties"],
  "if": {
    "properties": {
      "anchor": {
        "properties": {
          "propertyType": { "const": "123" }
        },
        "required": ["propertyType"]
      }
    }
  },
  "then": {
    "properties": {
      "setProperties": {
        "patternProperties": {
          "^[-&/_.:a-zA-Z0-9]+$": {
            "anyOf": [
              { "type": "string" },
              { "type": "number" },
              { "type": "boolean" }
            ]
          }
        },
        "additionalProperties": false
      }
    }
  },
  "else": {
    "properties": {
      "setProperties": {
        "patternProperties": {
          "^.*$": {
            "anyOf": [
              { "type": "string" },
              { "type": "number" },
              { "type": "boolean" }
            ]
          }
        },
        "additionalProperties": false
      }
    }
  }
}

• 把if/then/else移到顶层，这样才能读到同级的anchor.propertyType，判断逻辑才对。
• 在if里加了required，确保anchor里必须有propertyType，避免因属性缺失导致误判。
• 把Schema里的properties改成setProperties，和测试数据的键名对齐，让规则能作用到正确的对象上。
• 补了顶层对象的类型和必填字段，让Schema更严谨。

内容的提问来源于stack exchange，提问作者Atin Singh