autocomplete¶

Definition¶

autocomplete¶: The autocomplete operator performs a search for a word or phrase that contains a sequence of characters from an incomplete input string. You can use the autocomplete operator with search-as-you-type applications to predict words with increasing accuracy as characters are entered in your application's search field. autocomplete returns results that contain predicted words based on the tokenization strategy specified in the index definition for autocompletion. The fields that you intend to query with the autocomplete operator must be indexed with the autocomplete data type in the collection's index definition.

Syntax¶

autocomplete has the following syntax:

1 {
2   $search: {
3     "index": "<index name>", // optional, defaults to "default"
4     "autocomplete": {
5       "query": "<search-string>",
6       "path": "<field-to-search>",
7       "tokenOrder": "any|sequential",
8       "fuzzy": <options>,
9       "score": <options>
10     }
11   }
12 }

Options¶

Field

Type

Description

Necessity

Default

query

string or array of strings

String or strings to search for. If there are multiple terms in a string, Atlas Search also looks for a match for each term in the string separately.

yes

path

string

Indexed autocomplete type of field to search.

Tip

See also:

path construction

Note

The autocomplete operator does not support multi in the field path.

yes

fuzzy

object

Enable fuzzy search. Find strings which are similar to the search term or terms.

no

fuzzy

.maxEdits

integer

Maximum number of single-character edits required to match the specified search term. Value can be 1 or 2.

no

2

fuzzy

.prefixLength

integer

Number of characters at the beginning of each term in the result that must exactly match.

no

0

fuzzy

.maxExpansions

integer

Maximum number of variations to generate and search for. This limit applies on a per-token basis.

no

50

score

object

score assigned to matching search term results. Use one of the following options to modify the score:


`boost`	Multiply the result score by the given number.
`constant`	Replace the result score with the given number.

Note

autocomplete offers less fidelity in score in exchange for faster query execution.

no

tokenOrder

string

Order in which to search for tokens. Value can be one of the following:


`any`	Indicates tokens in the query can appear in any order in the documents. Results contain documents where the tokens appear sequentially and non-sequentially. However, results where the tokens appear sequentially score higher than other, non-sequential values.
`sequential`	Indicates tokens in the query must appear adjacent to each other or in the order specified in the query in the documents. Results contain only documents where the tokens appear sequentially.

no

any

Examples¶

The following examples use the movies collection in the sample_mflix database. If you loaded the sample dataset on your cluster, you can create the static index for autocompletion and run the queries on your cluster.

Click on your preferred tokenization strategy to view a sample index definition that you can use for the queries in the following examples:

Note

To learn more about edgeGram and nGram, see autocomplete.

You can follow the steps in the Tutorial: Create and Query an Atlas Search Index to load the sample dataset, create an index definition, and run Atlas Search queries.

Basic Examples¶

The following query searches for movies with the characters off in the title field. The query includes a:

$limit stage to limit the output to 10 results.
$project stage to exclude all fields except title.

1 db.movies.aggregate([
2   {
3     $search: {
4       "autocomplete": {
5         "path": "title",
6         "query": "off"
7       }
8     }
9   },
10   {
11     $limit: 10
12   },
13   {
14     $project: {
15       "_id": 0,
16       "title": 1
17     }
18   }
19 ])

Click on tokenization strategy to view the results:

Fuzzy Example¶

The following query searches for movies with the characters pre in the title field. The query uses:


Field	Description
`maxEdits`	Indicates that only one character variation is allowed in the query string `pre` to match the query to a word in the documents.
`prefixLength`	Indicates that the first character in the query string `pre` can't change when matching the query to a word in the documents.
`maxExpansions`	Indicates that up to two hundred and fifty six similar terms for `pre` can be considered when matching the query string to a word in the documents.

The query also includes a:

$limit stage to limit the output to 10 results.
$project stage to exclude all fields except title.

1 db.movies.aggregate([
2   {
3     $search: {
4       "autocomplete": {
5         "path": "title",
6         "query": "pre",
7         "fuzzy": {
8           "maxEdits": 1,
9           "prefixLength": 1,
10           "maxExpansions": 256
11         }
12       }
13     }
14   },
15   {
16     $project: {
17       "_id": 0,
18       "title": 1
19     }
20   }
21 ])

Click on tokenization strategy to view the results:

Token Order Example¶

The following queries search for movies with the characters men with in any and sequential order in the title field. The query includes a:

$limit stage to limit the output to 4 results.
$project stage to exclude all fields except title.

Give Feedback

← Operators compound →

1	{
2	$search: {
3	"index": "<index name>", // optional, defaults to "default"
4	"autocomplete": {
5	"query": "<search-string>",
6	"path": "<field-to-search>",
7	"tokenOrder": "any\|sequential",
8	"fuzzy": <options>,
9	"score": <options>
10	}
11	}
12	}

1	db.movies.aggregate([
2	{
3	$search: {
4	"autocomplete": {
5	"path": "title",
6	"query": "off"
7	}
8	}
9	},
10	{
11	$limit: 10
12	},
13	{
14	$project: {
15	"_id": 0,
16	"title": 1
17	}
18	}
19	])