Count Documents
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Overview
In this guide, you can learn how to retrieve accurate and estimated counts of the number of documents in a collection.
Sample Data
The examples in this guide use the movies collection in the sample_mflix
database from the Atlas sample datasets. To learn how to create a
free MongoDB Atlas cluster and load the sample datasets, see the
Get Started with Atlas guide.
The following Kotlin data class models the documents in this collection:
data class Movie( val id: ObjectId, val title: String )
Retrieve an Accurate Count
Use the countDocuments() method to count the number of documents that are in a
collection. To count the number of documents that match specified search
critera, pass a query filter to the countDocuments() method.
To learn more about specifying a query, see Specify a Query.
Count All Documents
To return a count of all documents in the collection, call the countDocuments() method
with no arguments, as shown in the following example:
println(collection.countDocuments())
21349
Count Specific Documents
To return a count of documents that match specific search criteria, specify your query
in the countDocuments() method. The following example prints a count of all documents
in the movies collection that have a year field value equal to 1930:
println(collection.countDocuments(eq("year", "1930")))
10
Customize Count Behavior
The countDocuments() method accepts optional parameters in the form of a
CountOptions object, which represents options you can use to configure the count
operation. You can set these options by instantiating a new CountOptions object,
setting the object's fields using the corresponding methods, and passing it to the
countDocuments() method. If you don't specify any options, the driver does not
customize the count operation.
The following table describes the options you can set to customize countDocuments():
Option | Description |
|---|---|
comment | Specifies a comment to attach to the operation. |
skip | Sets the number of documents to skip before returning results. |
limit | Sets the maximum number of documents to count. Must be a positive integer. |
maxTime | Sets the maximum amount of time to allow the operation to run, in milliseconds. |
collation | Specifies the kind of language collation to use when sorting
results. For more information, see Collation
in the MongoDB Server manual. |
hint | Sets the index to scan for documents. |
The following example uses a CountOptions object to add a comment to the
countDocuments() operation:
val options = CountOptions().comment("Retrieving count") collection.countDocuments(Filters.empty(), options)
Retrieve an Estimated Count
Use the estimatedDocumentCount() method to retrieve an estimate of the number of
documents in a collection. The method estimates the amount of documents based on
collection metadata, which can be faster than performing an accurate count.
The following example prints the estimated number of documents in a collection:
print(collection.estimatedDocumentCount())
21349
Customize Estimated Count Behavior
The estimatedDocumentCount() method accepts optional parameters in the form of an
EstimatedDocumentCountOptions object, which represents options you can use to configure
the count operation. You can set these options by instantiating a new
EstimatedDocumentCountOptions object, setting the object's fields using the
corresponding methods, and passing it to the estimatedDocumentCount() method.
If you don't specify any options, the driver does not customize the count operation.
The following table describes the options you can set to customize estimatedDocumentCount():
Option | Description |
|---|---|
comment | Specifies a comment to attach to the operation. |
maxTime | Specifies the maximum amount of time to allow the operation to run, in milliseconds. |
The following example uses an EstimatedDocumentCountOptions object to add a comment to
the estimatedDocumentCount() operation:
val options = EstimatedDocumentCountOptions().comment("Retrieving count") collection.estimatedDocumentCount(options)
API Documentation
To learn more about any of the methods or types discussed in this guide, see the following API documentation: