Normalizers

Normalizers are similar to analyzers except that they may only emit a single token. As a consequence, they do not have a tokenizer and only accept a subset of the available char filters and token filters. Only the filters that work on a per-character basis are allowed. For instance a lowercasing filter would be allowed, but not a stemming filter, which needs to look at the keyword as a whole. The current list of filters that can be used in a normalizer definition are: 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.

Elasticsearch ships with a lowercase built-in normalizer. For other forms of normalization, a custom configuration is required.

Custom normalizers take a list of character filters and a list of token filters.

 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" } } } }