使用转换函数对 AST 进行后处理以重命名 json 字段名称时出现奇怪的行为

Question

我很可能做错了，但事情就是这样。我正在使用 lift-json 将 json 响应字符串转换为对象。我得到的响应字符串有一些字段名称，这些名称不是在 Scala 中使用的最佳主意，即选项。我想编写一个“帮助器”函数，它几乎只是 JValue.transform 的包装器：

def renameFields(originalJson : JValue, oldFieldName : String, newFieldName : String): JValue = {
    originalJson transform { case JField(oldFieldName,x) => JField(newFieldName, x)}
}

这是我正在使用的示例响应字符串和 JObject：

scala> val jstring = """ { "aisle" : 1, "bin" : 1, "hasWhat" : [{ "id" : 4, "name" : "Granny", "color" : "green"}, { "id" : 4, "name" : "Fuji", "color" : "red"}] }"""
jstring: java.lang.String =  { "aisle" : 1, "bin" : 1, "hasWhat" : [{ "id" : 4, "name" : "Granny", "color" : "green"}, { "id" : 4, "name" : "Fuji", "color" : "red"}] }

scala> val json = parse(jstring)
json: net.liftweb.json.JsonAST.JValue = JObject(List(JField(aisle,JInt(1)), JField(bin,JInt(1)), JField(hasWhat,JArray(List(JObject(List(JField(id,JInt(4)), JField(name,JString(Granny)), JField(color,JString(green)))), JObject(List(JField(id,JInt(4)), JField(name,JString(Fuji)), JField(color,JString(red)))))))))

如果我使用此函数，所有字段名称最终都会更改：

scala> Util.renameFields(json,"aisle","row")
res2: net.liftweb.json.JsonAST.JValue = JObject(List(JField(row,JInt(1)), JField(row,JInt(1)), JField(row,JArray(List(JObject(List(JField(row,JInt(4)), JField(row,JString(Granny)), JField(row,JString(green)))), JObject(List(JField(row,JInt(4)), JField(row,JString(Fuji)), JField(row,JString(red)))))))))

而我真正想要的是：

scala> json transform { case JField("aisle",x) => JField("row",x) }
res3: net.liftweb.json.JsonAST.JValue = JObject(List(JField(row,JInt(1)), JField(bin,JInt(1)), JField(hasWhat,JArray(List(JObject(List(JField(id,JInt(4)), JField(name,JString(Granny)), JField(color,JString(green)))), JObject(List(JField(id,JInt(4)), JField(name,JString(Fuji)), JField(color,JString(red)))))))))

那么……我做错了什么？提前致谢。

-还是新手

Answer 1

我认为您缺少的只是 oldFieldName 周围的反引号：

scala> def renameFields(originalJson : JValue, oldFieldName : String, newFieldName : String): JValue = originalJson transform { case JField(`oldFieldName`,x) => JField(newFieldName, x)}
renameFields: (originalJson: net.liftweb.json.JsonAST.JValue,oldFieldName: String,newFieldName: String)net.liftweb.json.JsonAST.JValue

scala> val jstring = """ { "aisle" : 1, "bin" : 1, "hasWhat" : [{ "id" : 4, "name" : "Granny", "color" : "green"}, { "id" : 4, "name" : "Fuji", "color" : "red"}] }"""
jstring: java.lang.String =  { "aisle" : 1, "bin" : 1, "hasWhat" : [{ "id" : 4, "name" : "Granny", "color" : "green"}, { "id" : 4, "name" : "Fuji", "color" : "red"}] }

scala> val json = parse(jstring)
json: net.liftweb.json.JsonAST.JValue = JObject(List(JField(aisle,JInt(1)), JField(bin,JInt(1)), JField(hasWhat,JArray(List(JObject(List(JField(id,JInt(4)), JField(name,JString(Granny)), JField(color,JString(green)))), JObject(List(JField(id,JInt(4)), JField(name,JString(Fuji)), JField(color,JString(red)))))))))

scala> renameFields(json,"aisle","row")
res0: net.liftweb.json.JsonAST.JValue = JObject(List(JField(row,JInt(1)), JField(bin,JInt(1)), JField(hasWhat,JArray(List(JObject(List(JField(id,JInt(4)), JField(name,JString(Granny)), JField(color,JString(green)))), JObject(List(JField(id,JInt(4)), JField(name,JString(Fuji)), JField(color,JString(red)))))))))

如果没有反引号，case JField(oldFieldName,x) 会说“将我找到的任何值绑定为 JField 名称到新变量 oldFieldName”，因此您的原始 oldFieldName 变量被隐藏。通过 oldFieldName 周围的反引号，您表示您只想匹配名称为 oldFieldName 值的 JField。