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autocomplete

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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.

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}
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:
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

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 Get Started with Atlas Search to load the sample dataset, create an index definition, and run Atlas Search queries.

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

1db.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:

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:

1db.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:

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

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On this page

  • Definition
  • Syntax
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  • Examples