Elasticsearch experience非嵌套聚合报错：nested设置与brand、company复合聚合实现

• 核心规则：Elasticsearch 不允许对已存在数据的索引直接修改已有字段的类型，之前直接修改映射失败，就是因为违反了这个机制。要将数组对象字段设置为nested类型，必须走「新建带正确映射的索引+数据迁移」的流程：
  1. 创建新索引，在映射中显式将experience字段声明为nested类型，保留原有所有子字段的配置不变，示例创建命令：

  PUT user_data1_nested
  {
    "mappings": {
      "properties": {
        "creation_date": {"type": "date"},
        "current_position": {
          "properties": {
            "position": {"type": "text", "fields": {"keyword": {"type": "keyword", "ignore_above": 256}}},
            "position_category": {"type": "text", "fields": {"keyword": {"type": "keyword", "ignore_above": 256}}},
            "position_level": {"type": "long"}
          }
        },
        "experience": {
          "type": "nested",
          "properties": {
            "brand": {"type": "text", "fields": {"keyword": {"type": "keyword", "ignore_above": 256}}},
            "brand_segment": {"type": "text", "fields": {"keyword": {"type": "keyword", "ignore_above": 256}}},
            "company": {"type": "text", "fields": {"keyword": {"type": "keyword", "ignore_above": 256}}},
            "duration": {"type": "text", "fields": {"keyword": {"type": "keyword", "ignore_above": 256}}},
            "property_type": {"type": "text", "fields": {"keyword": {"type": "keyword", "ignore_above": 256}}},
            "real_estate_type": {"type": "text", "fields": {"keyword": {"type": "keyword", "ignore_above": 256}}}
          }
        },
        "id": {"type": "long"},
        "last_updation_date": {"type": "date"},
        "name": {"type": "text", "fields": {"keyword": {"type": "keyword", "ignore_above": 256}}},
        "profile_complition": {"type": "text", "fields": {"keyword": {"type": "keyword", "ignore_above": 256}}},
        "seeking_position": {
          "properties": {
            "position": {"type": "text", "fields": {"keyword": {"type": "keyword", "ignore_above": 256}}},
            "position_category": {"type": "text", "fields": {"keyword": {"type": "keyword", "ignore_above": 256}}},
            "position_level": {"type": "long"}
          }
        },
        "source": {"type": "text", "fields": {"keyword": {"type": "keyword", "ignore_above": 256}}}
      }
    },
    "settings": {
      "number_of_shards": 1,
      "number_of_replicas": 1
    }
  }
  

  2. 执行reindex命令，将旧索引user_data1中的全量文档迁移到新建的user_data1_nested索引中：

  POST _reindex
  {
    "source": {"index": "user_data1"},
    "dest": {"index": "user_data1_nested"}
  }
  

  3. 执行GET user_data1_nested/_mapping校验配置，确认experience字段的类型为nested即完成配置。

针对nested类型的字段做聚合，需要满足两个硬性要求：

1. 必须先通过nested聚合切入到对应的数组路径作用域，不能直接从顶层查询字段
2. 聚合时必须指定字段的keyword子字段（因为主字段是text类型，默认不支持聚合）

可直接运行的聚合查询如下：

GET user_data1_nested/_search
{
  "size": 0,
  "aggs": {
    "experience_nested_scope": {
      "nested": {"path": "experience"},
      "aggs": {
        "group_by_brand": {
          "terms": {"field": "experience.brand.keyword"},
          "aggs": {
            "group_by_company": {
              "terms": {"field": "experience.company.keyword"}
            }
          }
        }
      }
    }
  }
}

和普通object存储模式不同，nested类型会将每个experience数组元素作为独立的隐藏文档存储，能够严格保留单条记录内brand和company的绑定关系，不会出现字段值交叉错配的问题，可准确统计每个brand分组下对应的所有company的关联数据。

内容的提问来源于stack exchange，提问作者Richesh Chouksey