autocomplete Operator

Definition

autocomplete

The autocomplete operator performs a search for a word or phrase that contains a sequence of characters from an incomplete input string. 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. To learn how to configure your index for autocompletion, see How to Index Fields for Autocompletion.

Sample Use Cases

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.

If you want to build suggestions or dropdowns using the MongoDB Search autocomplete operator, we recommend that you query a collection of suggested search terms or use past search terms to populate the dropdown. If you create a separate collection of suggested search terms, you can define synonym mappings in your MongoDB Search index to search your collection for the exact or alternative words.

Syntax

autocomplete has the following syntax:

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{
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  $search: {
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    "index": "<index name>", // optional, defaults to "default"
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    "autocomplete": {
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      "query": "<search-string>",
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      "path": "<field-to-search>",
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      "tokenOrder": "any|sequential",
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      "fuzzy": <options>,
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      "score": <options>
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    }
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  }
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}

Options

Scoring Behavior

By default, the autocomplete operator uses the bm25 similarity algorithm to score documents depending on their relevance to the query.

You can change which similarity algorithm is used by specifying a different similarity algorithm in the similarity.type property for the autocomplete fields in your MongoDB Search index definition. To learn how to configure a MongoDB Search index for the autocomplete type, see How to Index Fields for Autocompletion.

To learn more about the supported similarity algorithms, see Score Details.

The autocomplete operator query results that are exact matches receive a lower score than results that aren't exact matches. MongoDB 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:

1. Index the field as both autocomplete and string types.

   MongoDB Search autocomplete boosts exact matches when an autocomplete field is also indexed as a string, thereby increasing the score of exact matches.

2. Query using the compound operator.

For a demonstration of this workaround, see Search Across Multiple Fields.

Examples

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{
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  "mappings": {
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    "dynamic": false,
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    "fields": {
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      "title": [
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        {
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          "type": "token"
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        },
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        {
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          "type": "string"
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        },
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        {
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          "foldDiacritics": false,
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          "maxGrams": 7,
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          "minGrams": 3,
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          "tokenization": "edgeGram",
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          "type": "autocomplete"
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        }
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      ],
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      "plot": [
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        {
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          "type": "autocomplete",
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          "tokenization": "edgeGram",
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          "minGrams": 2,
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          "maxGrams": 15,
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          "foldDiacritics": true
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        }
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      ]
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    }
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  }
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}

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{
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  "mappings": {
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    "dynamic": false,
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    "fields": {
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      "title": [
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        {
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          "type": "token"
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        },
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        {
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          "type": "string"
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        },
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        {
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          "foldDiacritics": false,
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          "maxGrams": 7,
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          "minGrams": 3,
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          "tokenization": "rightEdgeGram",
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          "type": "autocomplete"
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        }
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      ],
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      "plot": [
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        {
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          "type": "autocomplete",
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          "tokenization": "rightEdgeGram",
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          "minGrams": 2,
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          "maxGrams": 15,
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          "foldDiacritics": true
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        }
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      ]
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    }
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  }
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}

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{
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  "mappings": {
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    "dynamic": false,
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    "fields": {
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      "title": [
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        {
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          "type": "token"
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        },
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        {
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          "type": "string"
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        },
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        {
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          "foldDiacritics": false,
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          "maxGrams": 7,
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          "minGrams": 3,
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          "tokenization": "nGram",
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          "type": "autocomplete"
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        }
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      ],
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      "plot": [
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        {
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          "type": "autocomplete",
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          "tokenization": "nGram",
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          "minGrams": 2,
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          "maxGrams": 15,
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          "foldDiacritics": true
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        }
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      ]
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    }
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  }
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}

{
  "mappings": {
    "dynamic": false,
    "fields": {
      "title": [
      {
        "type": "token"
      },
      {
         "type": "string"
      },
      {
        "foldDiacritics": true,
        "maxGrams": 7,
        "minGrams": 3,
        "analyzer": "lucene.keyword",
        "tokenization": "edgeGram",
        "type": "autocomplete"
      }]
    }
  }
}

Learn More

To learn more, see How to Run Autocomplete and Partial Match MongoDB Search Queries.