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Multi fields

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Multi fields

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It is often useful to index the same field in Elasticsearch in different ways, to serve different purposes, for example, mapping a POCO string property as a string datatype for full text search as well as mapping as a not_analyzed string datatype for structured search, sorting and aggregations. Another example is mapping a POCO string property to use different analyzers, to serve different full text search needs.

public class Person
{
    public string Name { get; set; }
}

Creating Multi fields

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Let’s look at an example, using the following simple POCO

Multi fields can be created on a mapping using the .Fields() method within a field mapping

var descriptor = new CreateIndexDescriptor("myindex")
    .Mappings(ms => ms
        .Map<Person>(m => m
            .Properties(p => p
                .String(t => t
                    .Name(n => n.Name)
                    .Fields(ff => ff
                        .String(tt => tt
                            .Name("stop") 
                            .Analyzer("stop")
                        )
                        .String(tt => tt
                            .Name("shingles")
                            .Analyzer("name_shingles") 
                        )
                        .String(k => k
                            .Name("keyword") 
                            .IgnoreAbove(256)
                            .NotAnalyzed()
                        )
                    )
                )
            )
        )
    );

	Use the stop analyzer on this sub field
	Use a custom analyzer named "named_shingles" that is configured in the index
	Index as not analyzed

{
  "mappings": {
    "person": {
      "properties": {
        "name": {
          "type": "string",
          "fields": {
            "stop": {
              "type": "string",
              "analyzer": "stop"
            },
            "shingles": {
              "type": "string",
              "analyzer": "name_shingles"
            },
            "keyword": {
              "type": "string",
              "ignore_above": 256,
              "index": "not_analyzed"
            }
          }
        }
      }
    }
  }
}

Multi fields do not change the original _source field in Elasticsearch; they affect only how a field is indexed.

New multi fields can be added to existing fields using the Put Mapping API.

This is useful because the property can be used for both full text search as well as for structured search, sorting and aggregations

var searchResponse = client.Search<Person>(s => s
    .Query(q => q
        .Match(m => m
            .Field(f => f.Name)
            .Query("Russ Cam")
        ) && q
        .Match(m => m
            .Field(f => f.Name.Suffix("shingles")) 
            .Query("Russ Cam")
            .Boost(1.2)
        )
    )
    .Sort(ss => ss
        .Descending(f => f.Name.Suffix("keyword")) 
    )
    .Aggregations(a => a
        .Terms("peoples_names", t => t
            .Field(f => f.Name.Suffix("keyword"))
        )
    )
);

	Use the shingles subfield on `Name`
	Use the keyword subfield on `Name`

{
  "query": {
    "bool": {
      "must": [
        {
          "match": {
            "name": {
              "query": "Russ Cam"
            }
          }
        },
        {
          "match": {
            "name.shingles": {
              "query": "Russ Cam",
              "boost": 1.2
            }
          }
        }
      ]
    }
  },
  "sort": [
    {
      "name.keyword": {
        "order": "desc"
      }
    }
  ],
  "aggs": {
    "peoples_names": {
      "terms": {
        "field": "name.keyword"
      }
    }
  }
}

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