Scala Json Lift - 一條記錄的MappingException錯誤

Question

我在解析 json 時遇到問題。 僅當存在一組記錄時才會出現此問題，無論所有列都有值還是一列或多列為空值。 其他情況下它工作正常。

我的輸入案例類如下：

    case class Source(AccountNo: String, Name: String)
    case class HitsIndex(_index: String, _type: String, _id: String, _score: Double, _source: Source)
    case class HitsCount(total: Int, max_score: Double, hits: List[HitsIndex])
    case class Shards(total: Int, successful: Int, failed: Int, hits: HitsCount)
    case class ParseJson(took: Int, timed_out: Boolean, _shards: Shards)

導入語句：

import scala.collection.mutable._
import net.liftweb.json._
import net.liftweb.json.DefaultFormats
import net.liftweb.json.Serialization.write

下面是我測試的代碼：

 case class Uiresult(AccountNo: String, Name: String)

    val json = parse(jsonString)
    val elements = (json \\ "_source").children
    for (acct <- elements) {
      val m = acct.extract[Source]
      val res = write(Uiresult(m.accountNo,  (m.firstName.toString() + m.lastName.toString()))
      println(res)
    }

一條記錄的期望輸出：

注意：姓氏為空

[
{"AccountNo":"1234","Name":"Augustin "}
]

注意：所有列都有值

[
{"AccountNo":"1234","Name":"Augustin Wagstuff "}
]

但收到如下錯誤消息：

 > Exception in thread "main" net.liftweb.json.MappingException: No usable value for AccountNo
    Did not find value which can be converted into java.lang.String
        at net.liftweb.json.Meta$.fail(Meta.scala:191)
        at net.liftweb.json.Extraction$.mkValue$1(Extraction.scala:357)
        at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$build$1(Extraction.scala:317)
        at net.liftweb.json.Extraction$$anonfun$14.apply(Extraction.scala:253)
        at net.liftweb.json.Extraction$$anonfun$14.apply(Extraction.scala:253)
        at scala.collection.immutable.List.map(List.scala:273)
        at net.liftweb.json.Extraction$.instantiate$1(Extraction.scala:253)
        at net.liftweb.json.Extraction$.newInstance$1(Extraction.scala:286)
        at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$build$1(Extraction.scala:315)
        at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$extract0(Extraction.scala:366)
        at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$extract0(Extraction.scala:199)
        at net.liftweb.json.Extraction$.extract(Extraction.scala:43)
        at net.liftweb.json.JsonAST$JValue.extract(JsonAST.scala:312)
        at com.aexp.prospect.atul.sample_01.JsonRead$$anonfun$1.apply(JsonRead.scala:115)
        at com.aexp.prospect.atul.sample_01.JsonRead$$anonfun$1.apply(JsonRead.scala:114)
        at scala.collection.immutable.List.map(List.scala:273)
        at com.aexp.prospect.atul.sample_01.JsonRead$.main(JsonRead.scala:114)
        at com.aexp.prospect.atul.sample_01.JsonRead.main(JsonRead.scala)
    Caused by: net.liftweb.json.MappingException: Did not find value which can be converted into java.lang.String
        at net.liftweb.json.Meta$.fail(Meta.scala:191)
        at net.liftweb.json.Extraction$.convert(Extraction.scala:403)
        at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$build$1(Extraction.scala:314)
        at net.liftweb.json.Extraction$.mkValue$1(Extraction.scala:351)
        ... 16 more

我的輸入 Json：（姓氏為空）

注意：所有列都有值

{
  "took": 1,
  "timed_out": false,
  "_shards": {
    "total": 3,
    "successful": 3,
    "failed": 0
  },
  "hits": {
    "total": 1,
    "max_score": 2.2488084,
    "hits": [
      {
        "_index": "test_02",
        "_type": "test_type",
        "_id": "123456",
        "_score": 2.2488084,
        "_source": {
          "AccountNo": "06009625297",
          "firstName": "Augustin",
          "lastName": "Wagstuff "
        }
      }
    ]
  }
}   

注意：姓氏為空

{
  "took": 1,
  "timed_out": false,
  "_shards": {
    "total": 3,
    "successful": 3,
    "failed": 0
  },
  "hits": {
    "total": 1,
    "max_score": 2.2488084,
    "hits": [
      {
        "_index": "test_02",
        "_type": "test_type",
        "_id": "123456",
        "_score": 2.2488084,
        "_source": {
          "AccountNo": "06009625297",
          "firstName": "Augustin",
          "lastName": ""
        }
      }
    ]
  }
}   

Json 對象打印：

示例 1：
在這里，我注意到所有的列都有價值。 我只選擇了一組有問題的記錄。

json JObject(List(JField(took,JInt(1)),JField(timed_out,JBool(false)),JField(_shards,JObject(List(JField(total,JInt(3)),JField(successful,JInt(3)) )), JField(failed,JInt(0)))), JField(hits,JObject(List(JField(total,JInt(1)), JField(max_score,JDouble(2.2488084)), JField(hits,JArray(列表(JObject(List(JField(_index,JString(test_02)), JField(_type,JString(test_type)), JField(_id,JString(123456)), JField(_score,JDouble(2.2488084)), JField(_source, JObject(List(JField(AccountNo,JString(06009625297)), JField(firstName,JString(Augustin)), JField(lastName,JString()))))))))))))))

示例：2 在這里，我注意到 lastName 是空的。 我只選擇了一組有問題的記錄。 有人可以幫助我如何處理這種情況。

json JObject(List(JField(took,JInt(1)),JField(timed_out,JBool(false)),JField(_shards,JObject(List(JField(total,JInt(3)),JField(successful,JInt(3)) )), JField(failed,JInt(0)))), JField(hits,JObject(List(JField(total,JInt(1)), JField(max_score,JDouble(2.2488084)), JField(hits,JArray(列表(JObject(List(JField(_index,JString(test_02)), JField(_type,JString(test_type)), JField(_id,JString(123456)), JField(_score,JDouble(2.2488084)), JField(_source, JObject(List(JField(AccountNo,JString(06009625297)), JField(firstName,JString(Augustin)), JField(lastName,JString()))))))))))))))

輸入中有 2 個或更多記錄集的示例：

輸入有 2 組記錄（僅提取 2 個而不是 1 個）：這不會產生任何問題並產生所需的輸出。 如果您注意到第一條記錄與之前的示例相同：2 輸入但在這里它不會產生任何錯誤。

{
  "took": 1,
  "timed_out": false,
  "_shards": {
    "total": 3,
    "successful": 3,
    "failed": 0
  },
  "hits": {
    "total": 2,
    "max_score": 2.2488084,
    "hits": [
      {
        "_index": "test_02",
        "_type": "test_type",
        "_id": "123456",
        "_score": 2.2488084,
        "_source": {
          "AccountNo": "06009625297",
          "firstName": "Augustin",
          "lastName": "Wagstuff"
        },
               "hits": [
      {
        "_index": "test_02",
        "_type": "test_type",
        "_id": "789078",
        "_score": 2.2188084,
        "_source": {
          "AccountNo": "06009625297",
          "firstName": "Augustin",
          "lastName": "Jhonson"
        }
      }
    ]
  }
}

輸出：正如預期的那樣。

[
    {"AccountNo":"06009625297","Name":"Augustin Wagstuff "},
    {"AccountNo":"06009625297","Name":"Augustin Jhonson"},

    ]

代碼中的 acct 值：

當我嘗試在輸出中有一組記錄時在 acct 中顯示競爭（參考代碼中的變量）時，我只看到第一列，即使輸入中的所有其他列都具有有效值。

acct JField(AccountNo,JString(1234))

當我嘗試在輸出中有兩組記錄時在 acct 中顯示競爭（參考代碼中的變量）時，即使所有列都具有有效值，我也只看到第一列。

acct JField(_source,JObject(List(JField(AccountNo,JString(06009625297)), JField(firstName,JString(Augustin)),JField(lastName,JString(Wagstuff)))))

acct JField(_source,JObject(List(JField(AccountNo,JString(06009625297)), JField(firstName,JString(Augustin)),JField(lastName,JString(Jhonson)))))

我在迭代列表時懷疑這個問題。 請有人幫我解決。

Answer 1

我創建了一個代碼來處理有 1 個或零個輸入記錄。 2 個或更多記錄正在工作（感謝 Shaido）。 下面是代碼，有人可以建議，是否可以以更好的方式構造此代碼。

case class Source(AccountNo: fnameString, : String, lname: String)
case class HitsIndex(_index: String, _type: String, _id: String, _score: Double, _source: Source)
case class HitsCount(total: Int, max_score: Double, hits: List[HitsIndex])
case class Shards(total: Int, successful: Int, failed: Int)
case class ParseJson(took: Int, timed_out: Boolean, _shards: Shards, hits: HitsCount)

case class Uiresult(masterid: String, value: String)
case class ErrorMsg(searchType: String, error_message: String)

def formatResult(jsonString: String, searchType: String): String = {
  implicit val formats = DefaultFormats
  val json = JsonParser.parse(jsonString)

  val elements = (json \\ "_source").children
  if (elements.isEmpty == true) {
    implicit val formats = DefaultFormats
    return (List(write(ErrorMsg(searchType, "No Matching Record Found"))).mkString("[\n", ",\n", "\n]"))
  }
  if (json.extract[ParseJson].hits.total == 1) {
    val m = (json \\ "_source").extract[Source]
    val list = List(write(Uiresult(m.AccountNo.toString(), (m.fname.toString() + m.lname.toString() ))))
    return (list.mkString("[\n", ",\n", "\n]"))

  } else {
    val elements = (json \\ "_source").children
    val list = for (source <- elements) yield {
      println(" source " + source)
      val m = source.extract[Source]
      val list = List(write(Uiresult(m.AccountNo.toString(), (m.fname.toString() + m.lname.toString() ))))
    }
    return (list.mkString("[\n", ",\n", "\n]"))
  }
}

Answer 2

在Parse json 中使用了 Scala 中的 Liftweb 進行了類似的討論，但沒有可用的價值

當我使用lift-json_2.11版本為3.2.0時我也遇到了這個問題經過多次試驗最終我使用2.6.3版本解決了這個問題

<dependency>
    <groupId>net.liftweb</groupId>
    <artifactId>lift-json_2.11</artifactId>
    <version>2.6.3</version>
</dependency>