Elasticsearch

17 Jan 2019

Search (Search APIs)
- term query vs. match query
- most_fields query type
Analyze (Indices APIs)

https://habr.com/ru/post/280488 (in Russian)

Search (Search APIs)

https://www.elastic.co/guide/en/elasticsearch/guide/master/language-intro.html

https://www.elastic.co/guide/en/elasticsearch/reference/current/search-search.html

The search API allows you to execute a search query and get back search hits that match the query.

`term` query vs. `match` query

https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-term-query.html

The term query looks for the exact term in the field’s inverted index — it doesn’t know anything about the field’s analyzer. This makes it useful for looking up values in keyword fields, or in numeric or date fields. When querying full text fields, use the match query instead, which understands how the field has been analyzed.

=> term for queries is like keyword for string field datatypes.

`most_fields` query type

https://www.elastic.co/guide/en/elasticsearch/guide/master/most-fields.html

it’s used to combine the scores from all matching fields.

Analyze (Indices APIs)

https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-analyze.html

https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-analyze.html

Performs the analysis process on a text and return the tokens breakdown of the text.

language analyzers

https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-term-query.html

The default standard analyzer drops most punctuation, breaks up text into individual words, and lower cases them. For instance, the standard analyzer would turn the string “Quick Brown Fox!” into the terms [quick, brown, fox].

testing analyzers

https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-analyze.html

[Analyze] Can be used without specifying an index against one of the many built in analyzers.

say, using cURL:

$ curl \
  -X GET "http://username:password@localhost:9200/_analyze?pretty" \
  -H "Content-Type: application/json" \
  -d '{"analyzer":"standard","text":"apel"}'

$ curl \
  -X GET "http://username:password@localhost:9200/_analyze?pretty" \
  -H "Content-Type: application/json" \
  -d '{"analyzer":"indonesian","text":"apel"}'

multi-fields

https://www.elastic.co/guide/en/elasticsearch/reference/current/mapping-types.html#_multi_fields

It is often useful to index the same field in different ways for different purposes. This is the purpose of multi-fields. For instance, a string field could be mapped as a text field for full-text search, and as a keyword field for sorting or aggregations. Alternatively, you could index a text field with the standard analyzer, the english analyzer, and the french analyzer.

This is the purpose of multi-fields. Most datatypes support multi-fields via the fields parameter.

{
  "mappings": {
    "_doc": {
      "properties": {
        "description": {
          "type": "keyword",
          "fields": {
            "text": {
              "type": "text",
              "analyzer": "indonesian"
            }
          }
        }
      }
    }
  }
}

now it’s possible to use both fields in the samy query:

GET /_search
{
  "query": {
    "multi_match": {
      "type": "most_fields",
      "query": "barang",
      "fields": ["description", "description.text"]
    }
  }
}

https://www.elastic.co/guide/en/elasticsearch/reference/current/multi-fields.html

Multi-fields do not change the original _source field.

=> _source field contains only original indexed fields - there are no multi-fields and text values (if any) are not analyzed:

GET /_search
{
  "size": 100,
  "_source": ["description", "description.text"]
}

{
  "took": 18,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": 38999,
    "max_score": 1.0,
    "hits": [
      {
        "_index": "reika_shops-1547776421298845",
        "_type": "_doc",
        "_id": "37137675",
        "_score": 1.0,
        "_source": {
          "description": "Online M"
        }
      }
    ]
  }
}

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