最近在做指令碼重評分時，遇上了一個空值問題。查詢時painless指令碼中若遇到欄位中的值為空值就會報錯，本來想用 value == null 這種形式的判斷來判斷欄位值是否為空，然後過來掉，結果發現並不行，

以下時錯誤示範：

這個重評分的程式碼在defprice欄位全部都有值得時候執行正常，但是一旦出現沒有值得情況，就會報以下錯誤

{
  "error": {
    "root_cause": [{
      "type": "script_exception",
      "reason": "runtime error",
      "script_stack": [
        
 
"org.elasticsearch.index.fielddata.ScriptDocValues$Longs.get(ScriptDocValues.java:121)",
        "org.elasticsearch.index.fielddata.ScriptDocValues$Longs.getValue(ScriptDocValues.java:115)",
        "if(doc['cpinfo_youkewang.defprice'].value>0) {",
        "                                   ^---- HERE"
      ],
      
 
"script": "if(doc['cpinfo_youkewang.defprice'].value>0) {return 1.0/doc['cpinfo_youkewang.defprice'].value;} else return 0;",
      "lang": "painless"
    }],
    "type": "search_phase_execution_exception",
    "reason": "all shards failed",
    "phase": "query",
    "grouped": true,
    "failed_shards": [{
      
 
"shard": 0,
      "index": "aiso_20q2v1_detail_gasstation",
      "node": "NE8IhhppQKalVXnjU-axBQ",
      "reason": {
        "type": "script_exception",
        "reason": "runtime error",
        "script_stack": [
          "org.elasticsearch.index.fielddata.ScriptDocValues$Longs.get(ScriptDocValues.java:121)",
          "org.elasticsearch.index.fielddata.ScriptDocValues$Longs.getValue(ScriptDocValues.java:115)",
          "if(doc['cpinfo_youkewang.defprice'].value>0) {",
          "                                   ^---- HERE"
        ],
        "script": "if(doc['cpinfo_youkewang.defprice'].value>0) {return 1.0/doc['cpinfo_youkewang.defprice'].value;} else return 0;",
        "lang": "painless",
        "caused_by": {
          "type": "illegal_state_exception",
          "reason": "A document doesn't have a value for a field! Use doc[<field>].size()==0 to check if a document is missing a field!"
        }
      }
    }]
  },
  "status": 400
}

輾轉之後偶然看了下報錯資訊，發現報錯原因裡面有提示如何看是否為空值，

於是把程式碼改成以下就可以了：

"rescore": [{
    "window_size": 10000,
    "query": {
      "score_mode": "total",
      "rescore_query": {
        "function_score": {
          "script_score": {
            "script": "if(doc['cpinfo_youkewang.defprice'].size() > 0 && doc['cpinfo_youkewang.defprice'].value>0) {return 1.0/doc['cpinfo_youkewang.defprice'].value;} else return 0;"
          }
        }
      }
    }
  }],

就是用得提示中得doc[<field>].size()來判斷的。