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Counting

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  • Syntax
  • Options
  • Count Results
  • SEARCH_META Aggregation Variable
  • Examples

The Atlas Search count option adds a field to the metadata results document that displays a count of the search results for the query. You can use count to determine the size of the result set. You can use it in the $search or $searchMeta stage. You must use it in conjuction with the operators or collectors to display either the total number of documents or a lower bound on the number of documents that match the query.

MongoDB recommends using count with the $searchMeta stage to retrieve metadata results only for the query. To retrieve metadata results and query results using the $search stage, you must use the $$SEARCH_META variable. To learn more, see SEARCH_META Aggregation Variable.

Note

Atlas Search doesn't include the count results in the results for queries run with count in explain mode.

count has the following syntax:

{
"$searchMeta"|"$search": {
"index": "<index name>", // optional, defaults to "default"
"<operator>": {
<operator-specifications>
},
"count": {
"type": "lowerBound"|"total",
"threshold": <number-of-documents> //optional
}
}
}
Field
Type
Description
Required?
type
int

Type of count of the documents in the result set. Value can be one of the following:

  • lowerBound - for a lower bound count of the number of documents that match the query. You can set the threshold for the lower bound number.
  • total - for an exact count of the number of documents that match the query. If the result set is large, Atlas Search might take longer than for lowerBound to return the count.

If omitted, defaults to lowerBound.

no
threshold
int
Number of documents to include in the exact count if type is lowerBound. If omitted, defaults to 1000, which indicates that any number up to 1000 is an exact count and any number above 1000 is a rough count of the number of documents in the result.
no

The count document included in the results document contains the following integer fields:

Option
Description
lowerBound
Lower bound for this result set. This is returned only when a count of type lowerBound is requested.
total
Total count for this result set. This is returned only when a count of type total is requested.

When you run your query using the $search stage, Atlas Search stores the metadata results in the $$SEARCH_META variable and returns only the search results. You can use the $$SEARCH_META variable in all the supported aggregation pipeline stages to view the metadata results for your $search query.

Note

You can't use the $$SEARCH_META variable to retrieve metadata results for queries over sharded collections.

MongoDB recommends using the $$SEARCH_META variable only if you need both the search results and the metadata results. Otherwise, use the:

  • $search stage for just the search results.
  • $searchMeta stage for just the metadata results.
Example

Suppose an index on the released field in the sample_mflix.movies collection:

{
"mappings": {
"dynamic": false,
"fields": {
"released": {
"type": "date"
}
}
}
}

The following query searches for movies released near September 01, 2011 in the movies collection. The query requests a total count of the results. The query includes a:

  • $project stage to exclude all fields except title and released from the documents and to include the metadata results stored in the $$SEARCH_META variable as the value of a field named meta.
  • $limit stage to limit the output to 2 documents.
db.movies.aggregate([
{
"$search": {
"near": {
"path": "released",
"origin": ISODate("2011-09-01T00:00:00.000+00:00"),
"pivot": 7776000000
},
"count": {
"type": "total"
}
}
},
{
$project: {
"meta": "$$SEARCH_META",
"title": 1,
"released": 1
}
},
{
"$limit": 2
}
])

Atlas Search returns the following results for the query:

{
"_id" : ObjectId("573a13c3f29313caabd6b025"),
"title" : "Submarino",
"released" : ISODate("2011-09-01T00:00:00Z"),
"meta" : {
"count" : { "total" : NumberLong(23026) }
}
}
{
"_id" : ObjectId("573a13c7f29313caabd748f7"),
"title" : "Devil's Playground",
"released" : ISODate("2011-09-01T00:00:00Z"),
"meta" : {
"count" : { "total" : NumberLong(23026) }
}
}

To learn more about the results, see Count Results.

The following example uses an index on the year field in the sample_mflix.movies collection:

{
"mappings": {
"dynamic": false,
"fields": {
"year": {
"type": "number"
}
}
}
}
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