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Normalizer

The normalizer mapping parameter defines a custom normalization process for keyword fields. Unlike analyzers for text fields, which generate multiple tokens, normalizers transform the entire field value into a single token using a set of token filters. When you define a normalizer, the keyword field is processed by the specified filters before it is stored while keeping the _source of the document unchanged.

Defining a normalizer

The following request creates an index named products with a custom normalizer called my_normalizer. The normalizer is applied to the code field, which uses the trim and lowercase filters:

PUT /products
{
  "settings": {
    "analysis": {
      "normalizer": {
        "my_normalizer": {
          "type": "custom",
          "filter": ["trim", "lowercase"]
        }
      }
    }
  },
  "mappings": {
    "properties": {
      "code": {
        "type": "keyword",
        "normalizer": "my_normalizer"
      }
    }
  }
}

When you ingest a document into the index, the code field is normalized by trimming any extra spaces and converting the text to lowercase:

PUT /products/_doc/1
{
  "code": "  ABC-123 EXTRA  "
}

Search for the indexed document using lowercase and trimmed text in the query:

POST /products/_search
{
  "query": {
    "term": {
      "code": "abc-123 extra"
    }
  }
}

Because the code field is normalized, the term query successfully matches the stored document:

{
...
  "hits": {
    "total": {
      "value": 1,
      "relation": "eq"
    },
    "max_score": 0.2876821,
    "hits": [
      {
        "_index": "products",
        "_id": "1",
        "_score": 0.2876821,
        "_source": {
          "code": "  ABC-123 EXTRA  "
        }
      }
    ]
  }
}