Elastic search Nest C# - Is it possible a case insensitive sort on a string field through automap

Question

I have a elasticsearch Nest Model class

public class Data
    {       
        public long Id { get; set; }
       
        public string DeviceCode { get; set; }
    }

When indexing this document using automap, nest will create two fields for the property DeviceCode - DeviceCode and DeviceCode.keyword. I want to sort based on the DeviceCode.keyword field with case insensitive sorting - Is it possible to acheive this through automap (by applying analyser or filter using attribute mapping in the model class). I want to keep both text and keyword fields in elastic search.

Regards Vineeth

Answer 1

It's possible to apply a normalizer to a keyword field to lowercase values at index time for case-insensitive querying and aggregations

var client = new ElasticClient(settings);
    
var createIndexResponse = client.Indices.Create("my-data", c => c
    .Settings(s => s
        .Analysis(a => a
            .Normalizers(n => n
                .Custom("lowercase", cn => cn
                    .Filters("lowercase")
                )
            )
        )
    )
    .Map<Data>(m => m
        .AutoMap()
        .Properties(p => p
            .Text(t => t
                .Name(n => n.DeviceCode)
                .Fields(f => f
                    .Keyword(k => k
                        .Name("keyword")
                        .IgnoreAbove(256)
                    )
                    .Keyword(k => k
                        .Name("keyword_lowercase")
                        .Normalizer("lowercase")
                        .IgnoreAbove(256)
                    )
                )
            )
        )
    )
);

Then to use the keyword_lowercase multi-field

var searchResponse = client.Search<Data>(s => s
    .Index("my-data")
    .Sort(so => so
        .Ascending(f => f.DeviceCode.Suffix("keyword_lowercase"))
    )
);