Elasticsearch：normalizer

一、概述

‌Elastic normalizer‌是Elasticsearch中用于处理keyword类型字段的一种工具，主要用于对字段进行规范化处理，确保在索引和查询时保持一致性。

Normalizer与analyzer类似，都是对字段进行处理，但normalizer不会对字段进行分词，即没有tokenizer。它主要用于keyword类型的字段（不能再其他字段设置normalizer），可以在索引和查询时对字段值进行额外的处理，如转换为小写。例如，可以使用normalizer将字段值转换为小写，这在处理大小写不敏感的查询时非常有用‌。

二、normalizer的属性

normalizer仅仅有 char filters和token filters，具有的filter为：arabic_normalization, asciifolding, bengali_normalization, cjk_width, decimal_digit, elision, german_normalization, hindi_normalization, indic_normalization, lowercase, pattern_replace, persian_normalization, scandinavian_folding, serbian_normalization, sorani_normalization, trim, uppercase.
其中lowercase为Elasticsearch内置filter，其他的filter需要自定义配置。

自定义的chat filter和filter:

PUT index
{"settings": {"analysis": {"char_filter": {"quote": {"type": "mapping","mappings": ["« => \"","» => \""]}},"normalizer": {"my_normalizer": {"type": "custom","char_filter": ["quote"],"filter": ["lowercase", "asciifolding"]}}}},"mappings": {"properties": {"foo": {"type": "keyword","normalizer": "my_normalizer"}}}
}

三、验证只有keyword类型可以设置normalizer

创建如下mapping，并将类型为text的name字段设置上normalizer

PUT test_index
{"mappings": {"properties": {"name": {"type": "text","analyzer": "my_analyzer", "fields": {"keyword": {"type": "keyword","normalizer": "my_normalizer"}}},"title": {"type": "text","analyzer": "standard","fields": {"keyword": {"type": "keyword"}}}}},"settings": {"analysis": {"normalizer": {"my_normalizer": {"filter": ["lowercase"],"char_filter": []}},"analyzer": {"my_analyzer": {"filter":  ["lowercase"],"tokenizer": "standard"}}}}
}

提示如下错误信息：