autocomplete¶

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Definition
Syntax
Options
Examples

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:

{
  $search: {
    "autocomplete": {
      "query": "<search-string>",
      "path": "<field-to-search>",
      "tokenOrder": "any|sequential",
      "fuzzy": <options>,
      "score": <options>
    }
  }
}

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.

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.

edgeGram
nGram

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{
  "mappings": {
    "dynamic": false,
    "fields": {
      "title": [
        {
          "type": "autocomplete",
          "tokenization": "edgeGram",
          "minGrams": 3,
          "maxGrams": 7,
          "foldDiacritics": false
        }
      ]
    }
  }
}

copy

{
  "mappings": {
    "dynamic": false,
    "fields": {
      "title": [
        {
          "type": "autocomplete",
          "tokenization": "nGram",
          "minGrams": 3,
          "maxGrams": 7,
          "foldDiacritics": false
        }
      ]
    }
  }
}

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.

copy

db.movies.aggregate([
  {
    $search: {
      "autocomplete": {
        "path": "title",
        "query": "off"
      }
    }
  },
  {
    $limit: 10
  },
  {
    $project: {
      "_id": 0,
      "title": 1
    }
  }
])

Click on tokenization strategy to view the results:

edgeGram
nGram

{ "title" : "Off the Map" }
{ "title" : "Off and Running" }
{ "title" : "Benji: Off the Leash!" }
{ "title" : "An Officer and a Gentleman" }
{ "title" : "A Spell to Ward Off the Darkness" }
{ "title" : "Office Romance" }
{ "title" : "Office Killer" }
{ "title" : "Office Space" }
{ "title" : "Off Beat" }
{ "title" : "Official Rejection" }

In the above results, the characters off appears at the beginning of a word in all the titles.

{ "title" : "Come Have Coffee with Us" }
{ "title" : "A Spell to Ward Off the Darkness" }
{ "title" : "Remake, Remix, Rip-Off: About Copy Culture & Turkish Pop Cinema" }
{ "title" : "Benji: Off the Leash!" }
{ "title" : "A Coffee in Berlin" }
{ "title" : "An Officer and a Gentleman" }
{ "title" : "The Official Story" }
{ "title" : "The Officer's Ward" }
{ "title" : "Hands off Mississippi" }
{ "title" : "Romanoff and Juliet" }

In the above results, the characters off is present at different positions in the titles.

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.

copy

db.movies.aggregate([
  {
    $search: {
      "autocomplete": {
        "path": "title",
        "query": "pre",
        "fuzzy": {
          "maxEdits": 1,
          "prefixLength": 1,
          "maxExpansions": 256
        }
      }
    }
  },
  {
    $project: {
      "_id": 0,
      "title": 1
    }
  }
])

Click on tokenization strategy to view the results:

edgeGram
nGram

{ "title" : "Prelude to War" }
{ "title" : "Sitting Pretty" }
{ "title" : "Gentlemen Prefer Blondes" }
{ "title" : "The Parent Trap" }
{ "title" : "Premature Burial" }
{ "title" : "The President's Analyst" }
{ "title" : "Pretty Poison" }
{ "title" : "El castillo de la pureza" }
{ "title" : "Premiya" }
{ "title" : "All the President's Men" }

These results show the words that are predicted for the query string with one character modification and with the first character constant at the beginning of the word in all the titles.

{ "title" : "Les vampires" }
{ "title" : "He Who Gets Slapped" }
{ "title" : "Shanghai Express" }
{ "title" : "It Happened One Night" }
{ "title" : "The Scarlet Empress" }
{ "title" : "David Copperfield" }
{ "title" : "Prelude to War" }
{ "title" : "It Happened on Fifth Avenue" }
{ "title" : "Berlin Express" }
{ "title" : "Sitting Pretty" }

These results show the words that are predicted for the query string with one character modification at different positions in the words in the titles.

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.

any
sequential

copy

db.movies.aggregate([
  {
    $search: {
      "autocomplete": {
        "path": "title",
        "query": "men with",
        "tokenOrder": "any"
      }
    }
  },
  {
    $limit: 4
  },
  {
    $project: {
      "_id": 0,
      "title": 1
    }
  }
])

This query returns the following results for the edgeGram tokenization strategy:

{ "title" : "Men Without Women" }
{ "title" : "Men with Guns" }
{ "title" : "Men with Brooms" }
{ "title" : "Without Men" }

This query returns the following results for the nGram tokenization strategy:

{ "title" : "Men Without Women" }
{ "title" : "Men with Guns" }
{ "title" : "Men with Brooms" }
{ "title" : "Women Without Men" }

copy

db.movies.aggregate([
  {
    $search: {
      "autocomplete": {
        "path": "title",
        "query": "men with",
        "tokenOrder": "sequential"
      }
    }
  },
  {
    $limit: 4
  },
  {
    $project: {
      "_id": 0,
      "title": 1
    }
  }
])

This query returns the following results for the edgeGram tokenization strategy:

{ "title" : "Men Without Women" }
{ "title" : "Men with Guns" }
{ "title" : "Men with Brooms" }

This query returns the following results for the nGram tokenization strategy:

{ "title" : "Men Without Women" }
{ "title" : "Men with Guns" }
{ "title" : "Men with Brooms" }
{ "title" : "Women Without Men" }

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