ElasticSearch Keyword usage with a prefix search

Elastic Stack Elasticsearch
2

I'd have said use a Prefix query, but it sounds like you can't change the query type the UI library is producing. Maybe it has an option to issue a different query?

Otherwise you might want to look at the wildcard field type. Its full-length matches (keyword-style) are a bit slower than if you used a keyword field, but they work - plus it enables the efficient use of wildcard queries, including wildcards in the simple query string query. Only thing is, it just got introduced in 7.9 so you might need to upgrade.

This is what I ran:

PUT index1
{
  "settings": {
    "analysis": {
      "char_filter": {
        "space_remover": {
          "type": "mapping",
          "mappings": [
            "\\u0020=>"
          ]
        }
      },
      "normalizer": {
        "lower_case_normalizer": {
          "type": "custom",
          "char_filter": [
            "space_remover"
          ],
          "filter": [
            "lowercase"
          ]
        }
      }
    }
  },
  "mappings": {
      "properties": {
        "field3": {
          "type": "keyword",
          "normalizer": "lower_case_normalizer"
        },
        "field3_wildcard": {
          "type": "wildcard"
        }
      }
  }
}

So far, so good, I just introduce a wildcard field alongside your keyword field so we can play more easily.

POST index1/_doc
{
  "field3": "Louis George Maurice Adolphe (Roche)",
  "field3_wildcard": "Louis George Maurice Adolphe (Roche)"
}

GET index1/_search if you want to check it's been indexed.

POST index1/_search
{
  "query": {
    "simple_query_string": {
      "query": "\"Louis George Maurice Adolphe*\"",
      "fields": [  
        "field3_wildcard"
      ],
      "default_operator": "or"
    }
  }
}

That finds the document. Only thing I've changed is to add the * wildcard at the end, to indicate Louis George Maurice Adolphe is a prefix. This doesn't work with a keyword field because that needs an exact full match. "query": "\"Louis George Maurice Adolphe (Roche)\"", (exact match) also works with wildcard.

I think this fulfils

I have a requirement to be able to search a sentence as complete or with prefix

Though it requires *s added to your queries.