HasGroup

interface HasGroup<Document : Any> : Pipeline<Document> 

Pipeline implementing the $group stage.

Inheritors

• AggregationPipeline

Properties

context

@LowLevelApi
abstract val context: BsonContext

The context used to generate this pipeline.

Functions

group

open fun <Out : Any> group(block: AccumulationOperators<Document, Out>.() -> Unit): Pipeline<Out>

Combines multiple documents into a single document.

The resulting documents contain fields generated by accumulating all input documents. To learn more about accumulation operators, see AccumulationOperators.

Example

If we have users with an account balance, we can find out the total account balance of all users.

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

class Result(
    val totalBalance: Int,
)

users.aggregate()
    .group {
        Result::totalBalance sum of(User::balance)
    }

To see the list of available accumulation operators, see AccumulationOperators.

Performance

$group is a blocking stage, which causes the pipeline to wait for all input data to be retrieved for the blocking stage before processing the data. A blocking stage may reduce performance because it reduces parallel processing for a pipeline with multiple stages. A blocking stage may also use substantial amounts of memory for large data sets.

External resources

• Official documentation

reinterpret

@DangerousMongoApi
@LowLevelApi
abstract fun <New : Any> reinterpret(): Pipeline<New>

Changes the type of the returned document, with no type-safety.

toString

abstract override fun toString(): String

JSON representation of this pipeline.

withStage

@DangerousMongoApi
@LowLevelApi
abstract fun withStage(stage: BsonNode): Pipeline<Document>

Creates a new pipeline that expands on the current one by adding stage.

writeTo

@LowLevelApi
abstract fun writeTo(writer: BsonValueWriter)

Writes the entire pipeline into writer.