CountOperations¶

interface CountOperations<Document : Any> : BaseOperations

The different MongoDB operations related to counting documents.

Inheritors¶

MongoCollection

Properties¶

context¶

@LowLevelApi
abstract val context: BsonContext

The full BSON configuration, used by the DSL to generate queries.

For more information, see BsonContext.

Functions¶

count¶

abstract suspend fun count(): Long

Counts how many documents exist in the collection.

Implementation

This method, just like in mongosh, in syntax sugar for an aggregation pipeline using the countTo stage.

External resources

mongosh documentation

See also

countEstimated: Faster alternative when the result doesn't need to be exact.

abstract suspend fun count(options: CountOptions<Document>.() -> Unit = {}, predicate: FilterQuery<Document>.() -> Unit): Long

Counts how many documents match predicate in the collection.

Example

class User(
    val name: String,
    val age: Int,
)

collection.count {
    User::name eq "foo"
    User::age eq 10
}

Implementation

This method, just like in mongosh, in syntax sugar for an aggregation pipeline using the match and the countTo stages.

External resources

mongosh documentation

countEstimated¶

abstract suspend fun countEstimated(): Long

Counts all documents in the collection.

Implementation

This function reads collection metadata instead of actually counting through all documents. This makes it much more performant (almost no CPU nor RAM usage), but the count may be slightly out of date.

In particular, it may become inaccurate when:

there are orphaned documents in a shared cluster,
an unclean shutdown happened.

Views do not possess the required metadata. When this function is called on a view (either a MongoDB view or a filter logical view), a regular count is executed instead.

Example

class User(
    val name: String,
    val age: Int,
)

collection.countEstimated()

External resources

mongosh documentation

See also

count: Perform the count for real.

exists¶

open suspend fun exists(options: CountOptions<Document>.() -> Unit = {}, predicate: FilterQuery<Document>.() -> Unit): Boolean

Tests if there exists a document that matches predicate in the collection.

This method is a convenience function for calling count with a limit of 1.

Example

class User(
    val name: String,
    val age: Int,
)

collection.exists {
    User::name eq "foo"
    User::age eq 10
}