autocomplete

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Definition

Syntax
Options
Limitations
Examples
Index Definition
Basic Examples
Fuzzy Example
Token Order Example
Highlighting Example
Compound Example

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.
Note
Atlas Search might return inaccurate results for queries with more than three words in a single string.

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 or array of strings

Indexed autocomplete type of field to search.

Tip

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.

fuzzy

.maxEdits

integer

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

2

fuzzy

.prefixLength

integer

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

0

fuzzy

.maxExpansions

integer

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

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.

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.

any

Limitations

The autocomplete operator query results that are exact matches receive a lower score than results that aren't exact matches. Atlas Search can't determine if a query string is an exact match for an indexed text if you specify just the autocomplete-indexed token substrings. To score exact matches higher, try the following workaround:

Note

The following workaround doesn't guarantee higher scores for exact matches in all cases.

Index the field as both autocomplete and string types.
Atlas Search autocomplete boosts exact matches when an autocomplete field is also indexed as a string, thereby increasing the score of exact matches.
Query using the compound operator.

For a demonstration of this workaround, see Compound Example.

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 example queries on your cluster.

Tip

If you've already loaded the sample dataset, follow the Get Started with Atlas Search tutorial to create an index definition and run Atlas Search queries.

Index Definition

The following tabs contain sample index definitions for the edgeGram, rightEdgeGram, and nGram tokenization strategies.

➤ Use the Select your language drop-down menu to set the language of the example on this page.

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.

Note

Your Results May Vary

Atlas Search returns different results depending on the tokenization strategy configured in the autocompletion field of the index definition.

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.

Note

Your Results May Vary

Atlas Search returns different results depending on the tokenization strategy configured in the autocompletion field of the index definition.

Note

Your Results May Vary

Atlas Search returns different results depending on the tokenization strategy configured in the autocompletion field of the index definition.

Token Order Example

The following queries search for movies with the characters men with in the title field. The queries also use the tokenOrder field, which specifies whether the query searches for tokens in any order or in sequential order.

Each query includes a:

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

Highlighting Example

The following query searches for the characters ger in the title field of the movies collection, with the highlight option enabled for the title field.

The query includes a:

$limit stage to limit the output to 5 results.
$project stage to:
- return the document's score.
- exclude all fields except title.
- add a new field called highlights, which contains highlighting information.

Important

To highlight the autocomplete indexed version of a path, the autocomplete operator must be the only operator that uses that path in the query.

Note

Your Results May Vary

Atlas Search returns different results depending on the tokenization strategy configured in the autocompletion field of the index definition.

Compound Example

The following index definition indexes the title field as both autocomplete and string types.

The following query searches for the characters ball in the title field of the movies collection using the compound operator. The query specifies a preference for documents that contain ballroom in the title field.

The query includes a:

$limit stage to limit the output to 10 results.
$project stage to:
- return the document's score.
- exclude all fields except title.

← Use Operators and Collectors in Queries 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	}

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Definition

Note

Syntax

Options

Tip

See also:

Note

Note

Limitations

Note

Examples

Tip

Index Definition

Basic Examples

Note

Your Results May Vary

Fuzzy Example

Note

Your Results May Vary

Note

Your Results May Vary

Token Order Example

Highlighting Example

Important

Note

Your Results May Vary

Compound Example

autocomplete