[[search-as-you-type]]
=== Search-as-you-type field type
++++
<titleabbrev>Search-as-you-type</titleabbrev>
++++

The `search_as_you_type` field type is a text-like field that is optimized to
provide out-of-the-box support for queries that serve an as-you-type completion
use case. It creates a series of subfields that are analyzed to index terms
that can be efficiently matched by a query that partially matches the entire
indexed text value. Both prefix completion (i.e matching terms starting at the
beginning of the input) and infix completion (i.e. matching terms at any
position within the input) are supported.

When adding a field of this type to a mapping

[source,console]
--------------------------------------------------
PUT my-index-000001
{
  "mappings": {
    "properties": {
      "my_field": {
        "type": "search_as_you_type"
      }
    }
  }
}
--------------------------------------------------

This creates the following fields

[horizontal]

`my_field`::

    Analyzed as configured in the mapping. If an analyzer is not configured,
    the default analyzer for the index is used

`my_field._2gram`::

    Wraps the analyzer of `my_field` with a shingle token filter of shingle
    size 2

`my_field._3gram`::

    Wraps the analyzer of `my_field` with a shingle token filter of shingle
    size 3

`my_field._index_prefix`::

    Wraps the analyzer of `my_field._3gram` with an edge ngram token filter


The size of shingles in subfields can be configured with the `max_shingle_size`
mapping parameter. The default is 3, and valid values for this parameter are
integer values 2 - 4 inclusive. Shingle subfields will be created for each
shingle size from 2 up to and including the `max_shingle_size`. The
`my_field._index_prefix` subfield will always use the analyzer from the shingle
subfield with the `max_shingle_size` when constructing its own analyzer.

Increasing the `max_shingle_size` will improve matches for queries with more
consecutive terms, at the cost of larger index size. The default
`max_shingle_size` should usually be sufficient.

The same input text is indexed into each of these fields automatically, with
their differing analysis chains, when an indexed document has a value for the
root field `my_field`.

[source,console]
--------------------------------------------------
PUT my-index-000001/_doc/1?refresh
{
  "my_field": "quick brown fox jump lazy dog"
}
--------------------------------------------------
// TEST[continued]

The most efficient way of querying to serve a search-as-you-type use case is
usually a <<query-dsl-multi-match-query,`multi_match`>> query of type
<<query-dsl-match-bool-prefix-query,`bool_prefix`>> that targets the root
`search_as_you_type` field and its shingle subfields. This can match the query
terms in any order, but will score documents higher if they contain the terms
in order in a shingle subfield.

[source,console]
--------------------------------------------------
GET my-index-000001/_search
{
  "query": {
    "multi_match": {
      "query": "brown f",
      "type": "bool_prefix",
      "fields": [
        "my_field",
        "my_field._2gram",
        "my_field._3gram"
      ]
    }
  }
}
--------------------------------------------------
// TEST[continued]

[source,console-result]
--------------------------------------------------
{
  "took" : 44,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 0.8630463,
    "hits" : [
      {
        "_index" : "my-index-000001",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 0.8630463,
        "_source" : {
          "my_field" : "quick brown fox jump lazy dog"
        }
      }
    ]
  }
}
--------------------------------------------------
// TESTRESPONSE[s/"took" : 44/"took" : $body.took/]
// TESTRESPONSE[s/"max_score" : 0.8630463/"max_score" : $body.hits.max_score/]
// TESTRESPONSE[s/"_score" : 0.8630463/"_score" : $body.hits.hits.0._score/]

To search for documents that strictly match the query terms in order, or to
search using other properties of phrase queries, use a
<<query-dsl-match-query-phrase-prefix,`match_phrase_prefix` query>> on the root
field. A <<query-dsl-match-query-phrase,`match_phrase` query>> can also be used
if the last term should be matched exactly, and not as a prefix. Using phrase
queries may be less efficient than using the `match_bool_prefix` query.

[source,console]
--------------------------------------------------
GET my-index-000001/_search
{
  "query": {
    "match_phrase_prefix": {
      "my_field": "brown f"
    }
  }
}
--------------------------------------------------
// TEST[continued]

[[specific-params]]
==== Parameters specific to the `search_as_you_type` field

The following parameters are accepted in a mapping for the `search_as_you_type`
field and are specific to this field type

`max_shingle_size`::
+
--
(Optional, integer)
Largest shingle size to create. Valid values are `2` (inclusive) to `4`
(inclusive). Defaults to `3`.

A subfield is created for each integer between `2` and this value. For example,
a value of `3` creates two subfields: `my_field._2gram` and `my_field._3gram`

More subfields enables more specific queries but increases index size.
--

[[general-params]]
==== Parameters of the field type as a text field

The following parameters are accepted in a mapping for the `search_as_you_type`
field due to its nature as a text-like field, and behave similarly to their
behavior when configuring a field of the <<text,`text`>> data type. Unless
otherwise noted, these options configure the root fields subfields in
the same way.

<<analyzer,`analyzer`>>::

    The <<analysis,analyzer>> which should be used for
    `text` fields, both at index-time and at
    search-time (unless overridden by the
    <<search-analyzer,`search_analyzer`>>). Defaults to the default index
    analyzer, or the <<analysis-standard-analyzer,`standard` analyzer>>.

<<mapping-index,`index`>>::

    Should the field be searchable? Accepts `true` (default) or `false`.

<<index-options,`index_options`>>::

    What information should be stored in the index, for search and highlighting
    purposes. Defaults to `positions`.

<<norms,`norms`>>::

    Whether field-length should be taken into account when scoring queries.
    Accepts `true` or `false`. This option configures the root field
    and shingle subfields, where its default is `true`. It does not configure
    the prefix subfield, where it it `false`.

<<mapping-store,`store`>>::

    Whether the field value should be stored and retrievable separately from
    the <<mapping-source-field,`_source`>> field. Accepts `true` or `false`
    (default). This option only configures the root field, and does not
    configure any subfields.

<<search-analyzer,`search_analyzer`>>::

    The <<analyzer,`analyzer`>> that should be used at search time on
    <<text,`text`>> fields. Defaults to the `analyzer` setting.

<<search-quote-analyzer,`search_quote_analyzer`>>::

    The <<analyzer,`analyzer`>> that should be used at search time when a
    phrase is encountered. Defaults to the `search_analyzer` setting.

<<similarity,`similarity`>>::

    Which scoring algorithm or _similarity_ should be used. Defaults
    to `BM25`.

<<term-vector,`term_vector`>>::

    Whether term vectors should be stored for the field. Defaults to `no`. This option configures the root field and shingle
    subfields, but not the prefix subfield.


[[prefix-queries]]
==== Optimization of prefix queries

When making a <<query-dsl-prefix-query,`prefix`>> query to the root field or
any of its subfields, the query will be rewritten to a
<<query-dsl-term-query,`term`>> query on the `._index_prefix` subfield. This
matches more efficiently than is typical of `prefix` queries on text fields,
as prefixes up to a certain length of each shingle are indexed directly as
terms in the `._index_prefix` subfield.

The analyzer of the `._index_prefix` subfield slightly modifies the
shingle-building behavior to also index prefixes of the terms at the end of the
field's value that normally would not be produced as shingles. For example, if
the value `quick brown fox` is indexed into a `search_as_you_type` field with
`max_shingle_size` of 3, prefixes for `brown fox` and `fox` are also indexed
into the `._index_prefix` subfield even though they do not appear as terms in
the `._3gram` subfield. This allows for completion of all the terms in the
field's input.
