How to use the elastic word delimiter graph filter with synonyms

• https://www.elastic.co/guide/en/elasticsearch/reference/current/analysis-word-delimiter-graph-tokenfilter.html
• https://www.elastic.co/guide/en/elasticsearch/reference/current/analysis-synonym-graph-tokenfilter.html
• https://www.elastic.co/guide/en/elasticsearch/reference/current/analysis-multiplexer-tokenfilter.html

1. aproach

• the lowercase filter can not be applied before the word_delimiter_graph filter, because the word_delimiter_graph filter split on lower upper case transitions

PUT my_index

{
  "settings": {
    "analysis": {
      "analyzer": {
        "my_analyzer": {
          "tokenizer": "standard",
          "filter": [
            "my_word_delimiter_filter",
            "lowercase",
            "my_synonym_filter"
          ]
        }
      },
      "filter": {
        "my_word_delimiter_filter": {
          "type": "word_delimiter_graph",
          "generate_word_parts": true,
          "catenate_words": false
        },
        "my_synonym_filter": {
          "type": "synonym",
          "synonyms_path": "analysis/synonyms.txt"
        }
      }
    }
  }
}

• The problem: The synonym_graph filter can not be used after the word_delimiter_graph filter

{
  "error": {
    "root_cause": [
      {
        "type": "illegal_argument_exception",
        "reason": "Token filter [my_word_delimiter_filter] cannot be used to parse synonyms"
      }
    ],
    "type": "illegal_argument_exception",
    "reason": "Token filter [my_word_delimiter_filter] cannot be used to parse synonyms"
  },
  "status": 400
}

• In the elastic documentation it is answered why.
• https://www.elastic.co/guide/en/elasticsearch/reference/current/analysis-synonym-graph-tokenfilter.html

2. aproach

• use the synonym filter before the word_delimiter filter

{
  "filter": [
    "my_synonym_filter",
    "my_word_delimiter_filter",
    "lowercase"
  ]
}

Problem:

• Synonym gen,generation
• word: Gen
• the synonym is not applied because Gen is uppercase
• to have all synonyms in upper and lowercase is not an option

3. aproach - use a multiplexer

• https://www.elastic.co/guide/en/elasticsearch/reference/current/analysis-multiplexer-tokenfilter.html

PUT my_index

{
  "settings": {
    "analysis": {
      "analyzer": {
        "my_analyzer": {
          "tokenizer": "standard",
          "filter": [
            "my_word_delimiter_filter",
            "lowercase",
            "my_synonym_filter"
          ]
        }
      },
      "filter": {
                "my_multiplexer": {
          "type": "multiplexer",
          "filters": [  "delimiter_search_index, lowercase", 
                        "lowercase, Synonym Graph, query_stopwords, stem_override, Snowball, unique" 
                        ]
        },
        "my_word_delimiter_filter": {
          "type": "word_delimiter_graph",
          "generate_word_parts": true,
          "catenate_words": false
        },
        "my_synonym_filter": {
          "type": "synonym",
          "synonyms_path": "analysis/synonyms.txt"
        }
      }
    }
  }
}