C# Nest ElasticSearch Not able to map "token_chars" to Nest fluentMapping

Question

I have created below index through ElasticSearch Sense browser plugin, and also created C# Nest Fluent Mapping. I can express everything in Nest except "token_chars" on nGrams filter. I am not getting strongly typed property on C# nest to add "token_chars". Has anybody faced the same problem?

The json and c# settings are listed as below. Please help

        "analysis": {
           "analyzer": {
              "str_index_analyzer": {
                 "filter": [
                    "lowercase",
                    "substring"
                 ],
                 "tokenizer": "keyword"
              },
           "filter": {
              "substring": {
                 "max_gram": "50",
                 "type": "nGram",
                 "min_gram": "2",
                 "token_chars": [ /*Not able to map */
                    "letter",
                    "digit"
                 ]
              }
           }

I am not getting strongly typed property on C# nest to add "token_chars". Is anybody faced the same problem?

           var result = this._client.CreateIndex("mkfindex1", c => c
           .Analysis(a => a.Analyzers(an => an.Add("str_index_analyzer", new CustomAnalyzer()
            {
                Filter = new string[] { "lowercase", "substring" },
                Tokenizer = "keyword"
            })).TokenFilters(bases => bases.Add("substring", new NgramTokenFilter()
            {
                MaxGram = 50,
                MinGram = 2,

                /*"token_chars": [//Not able to map
                    "letter",
                    "digit"
                 */
             }))));

Answer 1

I have run into the same issue. The workaround for this is to not use the Fluent Mapping and just specify your analysis settings directly as Fluent Dictionary entries via the Settings.Add() method. Below is an example that should configure your index correctly.

 var result = this._client.CreateIndex("mkfindex1", c => c
     .Settings.Add("analysis.analyzer", "str_index_analyzer")
     .Settings.add("analysis.analyzer.str_index_analyzer.type", "custom")
     .Settings.add("analysis.analyzer.str_index_analyzer.tokenizer", "keyword")
     .Settings.Add("analysis.analyzer.str_index_analyzer.filter.0", "lowercase")
     .Settings.Add("analysis.analyzer.str_index_analyzer.filter.1", "substring")
     .Settings.add("analysis.filter.substring.type", "nGram")
     .Settings.add("analysis.filter.substring.min_gram", "2")
     .Settings.add("analysis.filter.substring.max_gram", "50")
     .Settings.add("analysis.filter.substring.token_chars.0", "letter")
     .Settings.add("analysis.filter.substring.token_chars.0", "digit")
   );

Hope this helps.