normalizer(归一化)

keyword* fields*（关键字字段） 的 normalizer（归一化）属性与 analyzer（分析器）类似,只不过它保证 analysis chain（分析链）生成单一的 token （词元）.

normalizer（归一化）应用于索引 keyword（关键字）之前,以及诸如在 [match](https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-match-query.html) query(匹配查询),查询解析器搜索 keyword fields（关键字字段）的时候.

curl -XPUT 'localhost:9200/index?pretty' -H 'Content-Type: application/json' -d'
{
  "settings": {
    "analysis": {
      "normalizer": {
        "my_normalizer": {
          "type": "custom",
          "char_filter": [],
          "filter": ["lowercase", "asciifolding"]
        }
      }
    }
  },
  "mappings": {
    "type": {
      "properties": {
        "foo": {
          "type": "keyword",
          "normalizer": "my_normalizer"
        }
      }
    }
  }
}
'
curl -XPUT 'localhost:9200/index/type/1?pretty' -H 'Content-Type: application/json' -d'
{
  "foo": "BÀR"
}
'
curl -XPUT 'localhost:9200/index/type/2?pretty' -H 'Content-Type: application/json' -d'
{
  "foo": "bar"
}
'
curl -XPUT 'localhost:9200/index/type/3?pretty' -H 'Content-Type: application/json' -d'
{
  "foo": "baz"
}
'
curl -XPOST 'localhost:9200/index/_refresh?pretty'
curl -XGET 'localhost:9200/index/_search?pretty' -H 'Content-Type: application/json' -d'
{
  "query": {
    "match": {
      "foo": "BAR"
    }
  }
}
'

上述查询与 documents（文档） 1 和 2 相匹配,这是因为在索引和查询的时候都将 BAR转换为了 bar.

{
  "took": $body.took,
  "timed_out": false,
  "_shards": {
    "total": 5,
    "successful": 5,
    "failed": 0
  },
  "hits": {
    "total": 2,
    "max_score": 0.2876821,
    "hits": [
      {
        "_index": "index",
        "_type": "type",
        "_id": "2",
        "_score": 0.2876821,
        "_source": {
          "foo": "bar"
        }
      },
      {
        "_index": "index",
        "_type": "type",
        "_id": "1",
        "_score": 0.2876821,
        "_source": {
          "foo": "BÀR"
        }
      }
    ]
  }
}

此外,keywords 在索引之前转换意味着聚合返回 normalised values（归一化的值）:

curl -XGET 'localhost:9200/index/_search?pretty' -H 'Content-Type: application/json' -d'
{
  "size": 0,
  "aggs": {
    "foo_terms": {
      "terms": {
        "field": "foo"
      }
    }
  }
}
'

返回

{
  "took": 43,
  "timed_out": false,
  "_shards": {
    "total": 5,
    "successful": 5,
    "failed": 0
  },
  "hits": {
    "total": 3,
    "max_score": 0.0,
    "hits": []
  },
  "aggregations": {
    "foo_terms": {
      "doc_count_error_upper_bound": 0,
      "sum_other_doc_count": 0,
      "buckets": [
        {
          "key": "bar",
          "doc_count": 2
        },
        {
          "key": "baz",
          "doc_count": 1
        }
      ]
    }
  }
}