Highlighting¶

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Syntax

Options
Examples
Output

The Atlas Search highlight option adds fields to the result set that display search terms in their original context. You can use it in conjunction with $search operators to display search terms as they appear in the returned documents, along with the adjacent text content (if any). highlight results are returned as part of the $meta field.

Tip

Syntax¶

highlight has the following syntax:

{
  $search: {
    "index": "<index name>", // optional, defaults to "default"
    "<operator>": { // may be ``search``, ``term``, ``compound``, or ``span``
      "query": "<search-string>",
      "path": "<field-to-search>"
    },
    "highlight": {
      "path": "<field-to-search>",
      "maxCharsToExamine": "<number-of-chars-to-examine>", // optional, defaults to 500,000
      "maxNumPassages": "<number-of-passages>" // optional, defaults to 5
    }
  }
},
{
  $project: {
    "highlights": { "$meta": "searchHighlights" } }
  }
}

Options¶

Field	Type	Description	Required?
`path`	string	Document field to search. The `path` field may contain: A string An array of strings A multi analyzer specification An array containing a combination of strings and multi analyzer specifications A wildcard character `*` See Path Construction for more information.	yes
`maxCharsToExamine`	int	Maximum number of characters to examine on a document when performing highlighting for a field. If omitted, defaults to `500,000`, which means that Atlas Search only examines the first 500,000 characters in the search field in each document for highlighting.	no
`maxNumPassages`	int	Number of high-scoring passages to return per document in the `highlights` results for each field. A passage is roughly the length of a sentence. If omitted, defaults to 5, which means that for each document, Atlas Search returns the top 5 highest-scoring passages that match the search text.	no

The "$meta": "searchHighlights" field contains the highlighted results. That field isn’t part of the original document, so it is necessary to use a $project pipeline stage to add it to the query output.

Examples¶

The following examples use a collection called fruit that contains the following documents:

{
  "_id" : 1,
  "type" : "fruit",
  "summary" : "Apple varieties",
  "description" : "Apples come in several varieties, including Fuji, Granny Smith, and Honeycrisp. The most popular varieties are McIntosh, Gala, and Granny Smith."
},
{
  "_id" : 2,
  "type" : "fruit",
  "summary" : "Banana",
  "description" : "Bananas are usually sold in bunches of five or six."
},
{
  "_id" : 3,
  "type" : "fruit",
  "summary" : "Pear varieties",
  "description" : "Bosc and Bartlett are the most common varieties of pears."
}

Note

One useful aspect of highlighting is that it reveals the original text returned by the search query, which may not be exactly the same as the search term. For example, if you use a language-specific analyzer, your text searches return all the stemmed variations of your search terms.

Another useful aspect of highlighting is that it can be used to highlight any field, inside or outside of the query path. For example, when you search for a term, you can perform highlighting for the query term on the query field and any other fields that you specify using the highlight option. To learn more, see Multi-Field Example below.

The fruit collection has an index definition that uses the english analyzer and dynamic field mappings.

{
  "analyzer": "lucene.english",
  "searchAnalyzer": "lucene.english",
  "mappings": {
    "dynamic": true
  }
}

Output¶

The highlights field is an array containing the following output fields:

Field	Type	Description
`path`	string	Document field which returned a match.
`texts`	array of objects	Each search match returns one or more objects, containing the matching text and the surrounding text (if any).
`texts.value`	string	Text from the field which returned a match.
`texts.type`	string	Returned value is either `hit` or `text`. Results of type `hit` contain the string which returned a match. Results of type `text` contain the text content adjacent to the matching string.
`score`	float	The score assigned to the `highlights` object. The `highlights` score is a measure of the relevance of the `highlights` object to the query. If multiple `highlights` objects are returned, the most relevant `highlights` object has the highest score.

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