Highlighting¶

On this page

Syntax

Options
Output
Examples
Basic Example
Advanced Example
Multi-Field Example
Wildcard Example

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.

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 documents	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	Type of result. Value can be one of the following: `hit` - The results contain the term that matched the query. `text` - The results contain the text content adjacent to the matching term.
`score`	float	Score assigned to the matching result. 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.

Examples¶

The examples on this page 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."
}

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

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

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.

Basic Example¶

The following query searches for variety and bunch in the description field of the fruit collection, with the highlight option enabled.

The $project pipeline stage restricts the output to the description field and adds a new field called highlights, which contains highlighting information.

db.fruit.aggregate([
  {
    $search: {
      "text": {
        "path": "description",
        "query": ["variety", "bunch"]
      },
      "highlight": {
        "path": "description"
      }
    }
  },
  {
    $project: {
      "description": 1,
      "_id": 0,
      "highlights": { "$meta": "searchHighlights" }
    }
  }
])

The query returns the following results:

{
  "description" : "Bananas are usually sold in bunches of five or six. ",
  "highlights" : [
    {
      "path" : "description",
      "texts" : [
        {
          "value" : "Bananas are usually sold in ",
          "type" : "text"
        },
        {
          "value" : "bunches",
          "type" : "hit"
        },
        {
          "value" : " of five or six. ",
          "type" : "text"
        }
      ],
      "score" : 1.2841906547546387
    }
  ]
}
{
  "description" : "Bosc and Bartlett are the most common varieties of pears.",
  "highlights" : [
    {
      "path" : "description",
      "texts" : [
        {
          "value" : "Bosc and Bartlett are the most common ",
          "type" : "text"
        },
        {
          "value" : "varieties",
          "type" : "hit"
        },
        {
          "value" : " of pears.",
          "type" : "text"
        }
      ],
      "score" : 1.2691514492034912
    }
  ]
}
{
  "description" : "Apples come in several varieties, including Fuji, Granny Smith, and Honeycrisp. The most popular varieties are McIntosh, Gala, and Granny Smith. ",
  "highlights" : [
    {
      "path" : "description",
      "texts" : [
        {
          "value" : "Apples come in several ",
          "type" : "text"
        },
        {
          "value" : "varieties",
          "type" : "hit"
        },
        {
          "value" : ", including Fuji, Granny Smith, and Honeycrisp. ",
          "type" : "text"
        }
      ],
      "score" : 1.0330637693405151
    },
    {
      "path" : "description",
      "texts" : [
        {
          "value" : "The most popular ",
          "type" : "text"
        },
        {
          "value" : "varieties",
          "type" : "hit"
        },
        {
          "value" : " are McIntosh, Gala, and Granny Smith. ",
          "type" : "text"
        }
      ],
      "score" : 1.0940992832183838
    }
  ]
}

The search term bunch returns a match on the document with _id: 2, because the description field contains the word bunches. The search term variety returns a match on the documents with _id: 3 and _id: 1, because the description field contains the word varieties.

Advanced Example¶

The following query searches for variety and bunch in the description field of the fruit collection, with the highlight option enabled, maximum number of characters to examine set to 40, and only 1 high-scoring passage to return per document.

The $project pipeline stage restricts the output to the description field and adds a new field called highlights, which contains highlighting information.

db.fruit.aggregate([
  {
    $search: {
      "text": {
        "path": "description",
        "query": ["variety", "bunch"]
      },
      "highlight": {
        "path": "description",
        "maxNumPassages": 1,
        "maxCharsToExamine": 40
      }
    }
  },
  {
    $project: {
      "description": 1,
      "_id": 0,
      "highlights": { "$meta": "searchHighlights" }
    }
  }
])

The query returns the following results:

{
  "description" : "Bananas are usually sold in bunches of five or six. ",
  "highlights" : [
    {
      "path" : "description",
      "texts" : [
        {
          "value" : "Bananas are usually sold in ",
          "type" : "text"
        },
        {
          "value" : "bunches",
          "type" : "hit"
        },
        {
          "value" : " of f",
          "type" : "text"
        }
      ],
      "score" : 1.313065767288208
    }
  ]
}
{
  "description" : "Bosc and Bartlett are the most common varieties of pears.",
  "highlights" : [ ]
}
{
  "description" : "Apples come in several varieties, including Fuji, Granny Smith, and Honeycrisp. The most popular varieties are McIntosh, Gala, and Granny Smith.",
  "highlights" : [
    {
      "path" : "description",
      "texts" : [
        {
          "value" : "Apples come in several ",
          "type" : "text"
        },
        {
          "value" : "varieties",
          "type" : "hit"
        },
        {
          "value" : ", includ",
          "type" : "text"
        }
      ],
      "score" : 0.9093900918960571
    }
  ]
}

The second document in the above results contains an empty highlights array even though the search field contains the search term varieties, because Atlas Search only examined 40 characters for highlighting. Similarly, the word includ is truncated because Atlas Search only examined 40 characters in the search field for highlighting. In the third document, although multiple passages contain the search term, Atlas Search returns only one passage in the highlights results because the query required only 1 passage per document in the highlights results.

Multi-Field Example¶

The following query searches for varieties in the description field of the fruit collection, with the highlight option enabled for both the description and summary fields.

The $project pipeline stage adds a new field called highlights, which contains highlighting information for the query term across all fields in the highlight option.

db.fruit.aggregate([
  {
    $search: {
      "text": {
        "path": "description",
        "query": "varieties"
      },
      "highlight": {
        "path": ["description", "summary" ]
      }
    }
  },
  {
    $project: {
      "description": 1,
      "summary": 1,
      "_id": 0,
      "highlights": { "$meta": "searchHighlights" }
    }
  }
])

The query returns the following results:

{
  "summary" : "Pear varieties",
  "description" : "Bosc and Bartlett are the most common varieties of pears.",
  "highlights" : [
    {
      "path" : "summary",
      "texts" : [
        {
          "value" : "Pear ",
          "type" : "text"
        },
        {
          "value" : "varieties",
          "type" : "hit"
        }
      ],
      "score" : 1.3891443014144897 },
    {
      "path" : "description",
      "texts" : [
        {
          "value" : "Bosc and Bartlett are the most common ",
          "type" : "text"
        },
        {
          "value" : "varieties",
          "type" : "hit"
        },
        {
          "value" : " of pears.",
          "type" : "text"
        }
      ],
      "score" : 1.2691514492034912
    }
  ]
}
{
  "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.",
  "highlights" : [
    {
      "path" : "summary",
      "texts" : [
        {
          "value" : "Apple ",
          "type" : "text"
        },
        {
          "value" : "varieties",
          "type" : "hit"
        }
      ],
      "score" : 1.3859853744506836
    },
    {
      "path" : "description",
      "texts" : [
        {
          "value" : "Apples come in several ",
          "type" : "text"
        },
        {
          "value" : "varieties",
          "type" : "hit"
        },
        {
          "value" : ", including Fuji, Granny Smith, and Honeycrisp. ",
          "type" : "text"
        }
      ],
      "score" : 1.0330637693405151
    },
    {
      "path" : "description",
      "texts" : [
        {
          "value" : "The most popular ",
          "type" : "text"
        },
        {
          "value" : "varieties",
          "type" : "hit"
        },
        {
          "value" : " are McIntosh, Gala, and Granny Smith.",
          "type" : "text"
        }
      ],
      "score" : 1.0940992832183838
    }
  ]
}

The search term varieties returns a match on documents with _id: 1 and _id: 3 because the query field description in both documents contains the query term varieties. In addition, the highlights array includes the summary field because the field contains the query term varieties.

Wildcard Example¶

The following query searches for the term varieties in fields that begin with des in the fruit collection, with the highlight option enabled for fields that begin with des.

The $project pipeline stage adds a new field called highlights, which contains highlighting information.

db.fruit.aggregate([
  {
    $search: {
      "text": {
        "path": {"wildcard": "des*"},
        "query": ["variety"]
      },
      "highlight": {
        "path": {"wildcard": "des*"}
      }
    }
  },
  {
    $project: {
      "description": 1,
      "_id": 0,
      "highlights": { "$meta": "searchHighlights" }
    }
  }
])

The query returns the following results. The fields that begin with des are highlighted.

{
  "description" : "Bosc and Bartlett are the most common varieties of pears.",
  "highlights" : [
    {
      "path" : "description",
      "texts" : [
        {
          "value" : "Bosc and Bartlett are the most common ",
          "type" : "text"
        },
        {
          "value" : "varieties",
          "type" : "hit"
        },
        {
          "value" : " of pears.",
          "type" : "text"
        }
      ],
      "score" : 1.2691514492034912 }
  ]
}
{
  "description" : "Apples come in several varieties, including Fuji, Granny Smith, and Honeycrisp. The most popular varieties are McIntosh, Gala, and Granny Smith.",
  "highlights" : [
    {
      "path" : "description",
      "texts" : [
        {
          "value" : "Apples come in several ",
          "type" : "text"
        },
        {
          "value" : "varieties",
          "type" : "hit"
        },
        {
          "value" : ", including Fuji, Granny Smith, and Honeycrisp. ",
          "type" : "text"
        }
      ],
      "score" : 1.0330637693405151
    },
    {
      "path" : "description",
      "texts" : [
        {
          "value" : "The most popular ",
          "type" : "text"
        },
        {
          "value" : "varieties",
          "type" : "hit"
        },
        {
          "value" : " are McIntosh, Gala, and Granny Smith.",
          "type" : "text"
        }
      ],
      "score" : 1.0940992832183838
    }
  ]
}