ElasticSearch中text字段的Painless过滤脚本无法运行问题

问题背景 #

需在Elasticsearch中通过Painless脚本实现text字段的精确匹配过滤，但该字段未启用fielddata且无法修改映射。尝试使用doc['my_field'] == 'MY_VALUE'时触发错误，提示找不到目标字段。

索引映射（不可修改） #

{
  "my_index": {
    "aliases": {},
    "mappings": {
      "properties": {
        "my_field": {
          "type": "text"
        }
      }
    },
    "settings": {
      "index": {
        "max_ngram_diff": "60",
        "number_of_shards": "8",
        "blocks": {
          "read_only_allow_delete": "false",
          "write": "false"
        },
        "analysis": {...}
      }
    }
  }
}

原查询及错误 #

原查询尝试结合match_phrase与脚本过滤：

{
    "size": 10,
    "index": "my_index",
    "body": {
        "query": {
            "bool": {
                "should": [{
                    "match_phrase": {
                        "my_field": {
                            "query": "MY_VALUE",
                            "boost": 1.5,
                            "slop": 0
                        }
                    }
                }],
                "must": [],
                "filter": [{
                    "script": {
                        "script": {
                            "lang": "painless",
                            "source": "doc['my_field'] == 'MY_VALUE'"
                        }
                    }
                }],
                "minimum_should_match": 1
            }
        }
    }
}

错误信息：

{
  "error": {
    "root_cause": [
      {
        "type": "script_exception",
        "reason": "runtime error",
        "script_stack": [
          "org.opensearch.search.lookup.LeafDocLookup.get(LeafDocLookup.java:101)",
          "org.opensearch.search.lookup.LeafDocLookup.get(LeafDocLookup.java:53)",
          "doc['my_field'] === 'MY_VALUE'",
          "    ^---- HERE"
        ],
        "script": "doc['my_field'] === 'MY_VALUE'",
        "lang": "painless",
        "position": {
          "offset": 4,
          "start": 0,
          "end": 30
        }
      }
    ],
    "type": "search_phase_execution_exception",
    "reason": "all shards failed",
    "phase": "query",
    "grouped": true,
    "failed_shards": [
      {
        "shard": 0,
        "index": "my_index",
        "node": "R99vOHeORlKsk9dnCzcMeA",
        "reason": {
          "type": "script_exception",
          "reason": "runtime error",
          "script_stack": [
            "org.opensearch.search.lookup.LeafDocLookup.get(LeafDocLookup.java:101)",
            "org.opensearch.search.lookup.LeafDocLookup.get(LeafDocLookup.java:53)",
            "doc['my_field'] === 'MY_VALUE'",
            "    ^---- HERE"
          ],
          "script": "doc['my_field'] === 'MY_VALUE'",
          "lang": "painless",
          "position": {
            "offset": 4,
            "start": 0,
            "end": 30
          },
          "caused_by": {
            "type": "illegal_argument_exception",
            "reason": "No field found for [my_field] in mapping with types []"
          }
        }
      }
    ]
  },
  "status": 400
}

原因分析 #

doc对象仅能访问带有doc values或fielddata的字段，而text类型字段默认不启用这两者，且无法修改映射开启，因此无法通过doc访问。

解决方案 #

改用_source对象直接获取原始字段值进行匹配，_source存储了文档的原始内容，无需额外配置。修改后的查询如下：

{
    "size": 10,
    "index": "my_index",
    "body": {
        "query": {
            "bool": {
                "should": [{
                    "match_phrase": {
                        "my_field": {
                            "query": "MY_VALUE",
                            "boost": 1.5,
                            "slop": 0
                        }
                    }
                }],
                "must": [],
                "filter": [{
                    "script": {
                        "script": {
                            "lang": "painless",
                            "source": "_source.my_field == 'MY_VALUE'"
                        }
                    }
                }],
                "minimum_should_match": 1
            }
        }
    }
}

注意事项 #

• 使用_source的性能略低于doc，因为需要加载整个文档的原始数据，但在无法修改映射的场景下是可行的替代方案。
• 确保_source字段未被禁用（默认启用），否则此方法无法生效。

内容的提问来源于stack exchange，提问作者Paolo Magnani