Elasticsearch match with stemming

Question

How do I do a search for a stemmed match?

I.e. at the moment I have many documents that contain the word "skateboard" in the item_title field, but only 3 documents that contain the word "skateboards". Because of this, when I do the following search:

POST /my_index/my_type/_search
{
    "size": 100,
    "query" : {
        "multi_match": {
           "query": "skateboards",
           "fields": [ "item_title^3" ]
        }
    }
}

I only get 3 results. However, I would like also documents with the word "skateboard" to be returned.

From what I understand from Elasticsearch I would expect that this is done by specifying a mapping on the item_title field that contains an analyser which indexes the stemmed version of each word, but I can't seem to find the documentation on how to do this, which suggests that it's done in a different way.

Suggestions?

Answer 1

Here's one example:

PUT /stem
{
  "settings": {
    "analysis": {
      "filter": {
        "filter_stemmer": {
          "type": "stemmer",
          "language": "english"
        }
      },
      "analyzer": {
        "tags_analyzer": {
          "type": "custom",
          "filter": [
            "standard",
            "lowercase",
            "filter_stemmer"
          ],
          "tokenizer": "standard"
        }
      }
    }
  },
  "mappings": {
    "test": {
      "properties": {
        "item_title": {
          "analyzer": "tags_analyzer",
          "type": "text"
        }
      }
    }
  }
}

Index some sample docs:

POST /stem/test/1
{
  "item_title": "skateboards"
}
POST /stem/test/2
{
  "item_title": "skateboard"
}
POST /stem/test/3
{
  "item_title": "skate"
}

Perform the query:

GET /stem/test/_search
{
  "query": {
    "multi_match": {
      "query": "skateboards",
      "fields": [
        "item_title^3"
      ]
    }
  },
  "fielddata_fields": [
    "item_title"
  ]
}

And see the results:

  "hits": [
     {
        "_index": "stem",
        "_type": "test",
        "_id": "1",
        "_score": 1,
        "_source": {
           "item_title": "skateboards"
        },
        "fields": {
           "item_title": [
              "skateboard"
           ]
        }
     },
     {
        "_index": "stem",
        "_type": "test",
        "_id": "2",
        "_score": 1,
        "_source": {
           "item_title": "skateboard"
        },
        "fields": {
           "item_title": [
              "skateboard"
           ]
        }
     }
  ]

I have added, also, the fielddata_fields element so that you can see how the content of the field has been indexed. As you can see, in both cases, the indexed term is skateboard.