Score the Documents in the Results

Usage

To include the score of each document in your search results, use the $project stage in your aggregation pipeline.

• For the $search stage, the score field takes the $meta expression, which requires the searchScore value. You can also specify the searchScoreDetails value for the scoreDetails field $meta expression for a detailed breakdown of the score.

  Note

  If you deployed Search Nodes, consider the following:

  • Avoid sorting the results by searchScore because it can be different across Search Nodes.

  • To calculate searchScore, a host takes into consideration all the documents that exist on it, including deleted documents that have not yet been removed from the index. Since the deletion occurs independently on each host, this might cause changes in searchScore depending on which host the query is routed to.

  To support pagination when sorting by searchScore on Search Nodes, upvote this request in the MongoDB Feedback Engine.

• For the $vectorSearch stage, the score field takes the $meta expression, which requires the vectorSearchScore value to return the score of each document in your vector search results.

1
db.movies.aggregate([
2
  {
3
    "$search": {
4
      "text": {
5
        <operator-specification>
6
      }
7
    }
8
  },
9
  {
10
    "$project": {
11
      "<field-to-include>": 1,
12
      "<field-to-exclude>": 0,
13
      "score": { "$meta": "searchScore" }
14
    }
15
  }
16
])

1
db.movies.aggregate([
2
  {
3
    "$search": {
4
      "text": {
5
        <operator-specification>
6
      },
7
      "scoreDetails": true
8
    }
9
  },
10
  {
11
    "$project": {
12
      "<field-to-include>": 1,
13
      "<field-to-exclude>": 0,
14
      "scoreDetails": { "$meta": "searchScoreDetails" }
15
    }
16
  }
17
])

1
db.movies.aggregate([
2
  {
3
    "$vectorSearch": {
4
      <query-syntax>
5
    }
6
  },
7
  {
8
    "$project": {
9
      "<field-to-include>": 1,
10
      "<field-to-exclude>": 0,
11
      "score": { "$meta": "vectorSearchScore" }
12
    }
13
  }
14
])

Behavior

The score assigned to a returned document is part of the document's metadata. You can use a $project stage in your aggregation pipeline to include each returned document's score along with the result set. Documents return from highest score to lowest. Many factors can influence a document's score, including the following:

• Position of the search term in the document.

• Frequency of occurrence of the search term in the document.

• Type of operator or analyzer an Atlas Search query uses.

To learn more about the Lucene scoring algorithm, see Lucene documentation.

Tutorials