您可以使用脚本字段来完成此操作。首先，让我们创建一个示例文档

POST sample-index/_doc
{
  "id": 1,
  "text": "Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged."
}

现在，让我们使用脚本字段执行查询：

GET sample-index/_search
{
  "_source": ["id"], 
  "query": {
    "match": {
      "text": "ipsum"
    }
  },
  "script_fields": {
    "text_summary": {
      "script": "if (params['_source']['text'].length() > 40) { return params['_source']['text'].substring(0,40) + '...'; } else { return  params['_source']['text']; }"
    }
  }
}

结果会是这样的：

{
  "took": 15,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": {
      "value": 1,
      "relation": "eq"
    },
    "max_score": 0.39556286,
    "hits": [
      {
        "_index": "sample-index",
        "_id": "ZAhIEoUBNMHtGSRnO4bt",
        "_score": 0.39556286,
        "_ignored": [
          "text.keyword"
        ],
        "_source": {
          "id": 1
        },
        "fields": {
          "text_summary": [
            "Lorem Ipsum is simply dummy text of the ..."
          ]
        }
      }
    ]
  }
}