Elasticsearch painless脚本中空值的检查

最近在做脚本重评分时，遇上了一个空值问题。查询时painless脚本中若遇到字段中的值为空值就会报错，本来想用 value == null 这种形式的判断来判断字段值是否为空，然后过来掉，结果发现并不行，

以下时错误示范：

这个重评分的代码在defprice字段全部都有值得时候运行正常，但是一旦出现没有值得情况，就会报以下错误

{
  "error": {
    "root_cause": [{
      "type": "script_exception",
      "reason": "runtime error",
      "script_stack": [
        "org.elasticsearch.index.fielddata.ScriptDocValues$Longs.getScriptDocValues.java:121)",
        "org.elasticsearch.index.fielddata.ScriptDocValues$Longs.getValueScriptDocValues.java:115)",
        "ifdoc['cpinfo_youkewang.defprice'].value>0) {",
        "                                   ^---- HERE"
      ],
      "script": "ifdoc['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$Longs.getScriptDocValues.java:121)",
          "org.elasticsearch.index.fielddata.ScriptDocValues$Longs.getValueScriptDocValues.java:115)",
          "ifdoc['cpinfo_youkewang.defprice'].value>0) {",
          "                                   ^---- HERE"
        ],
        "script": "ifdoc['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
}

辗转之后偶然看了下报错信息，发现报错原因里面有提示如何看是否为空值，

于是把代码改成以下就可以了：

"rescore": [{
    "window_size": 10000,
    "query": {
      "score_mode": "total",
      "rescore_query": {
        "function_score": {
          "script_score": {
            "script": "ifdoc['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)来判断的。

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