数组如何在ElasticSearch中索引

一、简介

在ElasticSearch里没有专门的数组类型，任何一个字段都可以有零个和多个值。当字段值的个数大于1时，字段类型就变成了数组。

下面以视频数据为例，介绍ElasticSearch如何索引数组数据，以及如何检索数组中的字段值。

测试视频数据格式如下：

{
    "media_id": 88992211,
    "tags": ["电影","科技","恐怖","电竞"]
}
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media_id代表视频id，tags是视频的标签，有多个值。业务上需要按视频标签检索标签下所有的视频。同一个视频有多个标签。

演示使用的ElasticSearch集群的版本是7.6.2。

二、测试演示

2.1 创建索引

PUT test_arrays
{
  "settings": {
    "number_of_shards": 1
  },
  "mappings": {
    "properties": {
      "media_id": {
        "type": "long"
      },
      "tags": {
        "type": "text"
      }
    }
  }
}
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2.2 向test_arrays索引里写入测试数据

POST test_arrays/_doc
{
  "media_id": 887722,
  "tags": [
      "电影",
      "科技",
      "恐怖",
      "电竞"
    ]
}
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2.3 查看test_arrays内部如何索引tags字段

{
  "tokens" : [
    {
      "token" : "电",
      "start_offset" : 0,
      "end_offset" : 1,
      "type" : "<IDEOGRAPHIC>",
      "position" : 0
    },
    {
      "token" : "影",
      "start_offset" : 1,
      "end_offset" : 2,
      "type" : "<IDEOGRAPHIC>",
      "position" : 1
    },
    {
      "token" : "科",
      "start_offset" : 3,
      "end_offset" : 4,
      "type" : "<IDEOGRAPHIC>",
      "position" : 102
    },
    {
      "token" : "技",
      "start_offset" : 4,
      "end_offset" : 5,
      "type" : "<IDEOGRAPHIC>",
      "position" : 103
    },
    {
      "token" : "恐",
      "start_offset" : 6,
      "end_offset" : 7,
      "type" : "<IDEOGRAPHIC>",
      "position" : 204
    },
    {
      "token" : "怖",
      "start_offset" : 7,
      "end_offset" : 8,
      "type" : "<IDEOGRAPHIC>",
      "position" : 205
    },
    {
      "token" : "电",
      "start_offset" : 9,
      "end_offset" : 10,
      "type" : "<IDEOGRAPHIC>",
      "position" : 306
    },
    {
      "token" : "竞",
      "start_offset" : 10,
      "end_offset" : 11,
      "type" : "<IDEOGRAPHIC>",
      "position" : 307
    }
  ]
}
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从响应结果可以看到，tags数组中的每个值被分词成多个token。

2.4 检索tags数组中的值

POST test_arrays/_search
{
  "query": {
    "match": {
      "tags": "电影"
    }
  }
}
响应结果：
{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 0.68324494,
    "hits" : [
      {
        "_index" : "test_arrays",
        "_type" : "_doc",
        "_id" : "MyhnpXQBGXOapfjvSpOW",
        "_score" : 0.68324494,
        "_source" : {
          "media_id" : 887722,
          "tags" : [
            "电影",
            "科技",
            "恐怖",
            "电竞"
          ]
        }
      }
    ]
  }
}

模糊检索：
POST test_arrays/_search
{
  "query": {
    "match": {
      "tags": "影"
    }
  }
}
响应结果
{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 0.2876821,
    "hits" : [
      {
        "_index" : "test_arrays",
        "_type" : "_doc",
        "_id" : "MyhnpXQBGXOapfjvSpOW",
        "_score" : 0.2876821,
        "_source" : {
          "media_id" : 887722,
          "tags" : [
            "电影",
            "科技",
            "恐怖",
            "电竞"
          ]
        }
      }
    ]
  }
}
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视频数据业务上需要通过标签精确匹配，查询标签下的所有视频。实现这种效果，需要把tags字段类型修改为keyword。test_arrays索引的mappings设置如下：

PUT test_arrays
{
  "settings": {
    "number_of_shards": 1
  },
  "mappings": {
    "properties": {
      "media_id": {
        "type": "long"
      },
      "tags": {
        "type": "keyword"
      }
    }
  }
}
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此时tags字段数组中每一个值对应一个token，可以实现按标签精准查询标签下视频的效果。

{
  "tokens" : [
    {
      "token" : "电影",
      "start_offset" : 0,
      "end_offset" : 2,
      "type" : "word",
      "position" : 0
    },
    {
      "token" : "科技",
      "start_offset" : 3,
      "end_offset" : 5,
      "type" : "word",
      "position" : 1
    },
    {
      "token" : "恐怖",
      "start_offset" : 6,
      "end_offset" : 8,
      "type" : "word",
      "position" : 2
    },
    {
      "token" : "电竞",
      "start_offset" : 9,
      "end_offset" : 11,
      "type" : "word",
      "position" : 3
    }
  ]
}
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实际业务场景中，视频标签的数据可能不是按数组存储的，全部标签存储在一个字符串中，标签之间用逗号分隔。

{
    "media_id": 88992211,
    "tags": "电影,科技,恐怖,电竞"
}

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上面的标签存储格式，通过调整索引字段的类型，同样可以实现精准检索单个标签下视频的效果。test_arrays索引的配置如下：

PUT test_arrays
{
  "settings": {
    "number_of_shards": 1,
    "analysis" : {
        "analyzer" : {
          "comma_analyzer": {
            "tokenizer": "comma_tokenizer"
          }
        },
        "tokenizer" : {
          "comma_tokenizer": {
            "type": "simple_pattern_split",
            "pattern": ","
          }
        }
      }
  },
  "mappings": {
    "properties": {
      "media_id": {
        "type": "long"
      },
      "tags": {
        "search_analyzer" : "simple",
        "analyzer" : "comma_analyzer",
        "type" : "text"
      }
    }
  }
}
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写入一条测试数据到test_arrays索引

POST test_arrays/_doc
{
  "media_id": 887722,
  "tags": "电影,科技,恐怖,电竞"
}
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tags字段的索引结构如下，同样实现了一个标签对应一个token。

{
  "tokens" : [
    {
      "token" : "电影",
      "start_offset" : 0,
      "end_offset" : 2,
      "type" : "word",
      "position" : 0
    },
    {
      "token" : "科技",
      "start_offset" : 3,
      "end_offset" : 5,
      "type" : "word",
      "position" : 1
    },
    {
      "token" : "恐怖",
      "start_offset" : 6,
      "end_offset" : 8,
      "type" : "word",
      "position" : 2
    },
    {
      "token" : "电竞",
      "start_offset" : 9,
      "end_offset" : 11,
      "type" : "word",
      "position" : 3
    }
  ]
}
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通过标签精准匹配查询。

请求参数
POST test_arrays/_search
{
  "query": {
    "match": {
      "tags": "电影"
    }
  }
}
响应结果
{
  "took" : 6,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 0.2876821,
    "hits" : [
      {
        "_index" : "test_arrays",
        "_type" : "_doc",
        "_id" : "3i2ipXQBGXOapfjv3THH",
        "_score" : 0.2876821,
        "_source" : {
          "media_id" : 887722,
          "tags" : "电影,科技,恐怖,电竞"
        }
      }
    ]
  }
}
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三、总结

ElasticSearch采用的一种数据类型同时支持单值和多值的设计理念，即简化了数据类型的总量，同时也降低索引配置的复杂度，是一种非常优秀的设计。