Transformation Pipeline Stages

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On this page, you will find a comprehensive list of transformation pipeline stages and their options.

Transformation Pipeline Stages

Stage Name	Description
`$addFields`	Adds new fields to documents.
`$bucket`	Groups documents into specified buckets based on an expression and boundaries. Options available.
`$bucketAuto`	Automatically distributes documents into a specified number of even buckets. Options available.
`$changeStream`	Returns a Change Stream cursor; must be the first stage in the pipeline.
`$collStats`	Provides statistics about a collection or view.
`$count`	Counts the documents at this pipeline stage.
`$currentOp`	Displays active and/or dormant operations. Requires the db.aggregate() method. Options available.
`$facet`	Executes multiple aggregation pipelines in one stage, enabling multi-faceted aggregations.
`$geoNear`	Orders documents based on geospatial proximity, incorporating $match, $sort, and $limit. Options available.
`$graphLookup`	Conducts a recursive search, appending results to the output document as an array. Options available.
`$group`	Groups documents by an expression, applying accumulator expressions to each group.
`$indexStats`	Reports usage statistics for each index in the collection.
`$limit`	Passes the first n documents unmodified to the pipeline.
`$listLocalSessions`	Lists active sessions on the connected mongos or mongod instance.
`$listSessions`	Lists sessions propagated to the system.sessions collection.
`$lookup`	Performs a left outer join with another collection in the same database. Options available.
`$match`	Filters documents, passing only matches to the next stage.
`$merge`	Writes aggregation results to a collection; must be the last stage in the pipeline. Options available.
`$out`	Writes aggregation results to a collection; must be the last stage. Options available.
`$planCacheStats`	Provides plan cache data for a collection.
`$project`	Reshapes each document, adding or removing fields.
`$redact`	Reshapes documents based on their content, allowing field level redaction.
`$replaceRoot`	Replaces a document with a specified embedded one, promoting the embedded document.
`$replaceWith`	Alias for `$replaceRoot`. Replaces a document with a specified embedded one.
`$sample`	Randomly selects a specified number of documents. Options available.
`$search`	Executes a full-text search.
`$set`	Alias for `$addFields`. Adds new fields to documents.
`$skip`	Skips the first n documents, passing the rest unmodified.
`$sort`	Reorders documents based on a specified sort key.
`$sortByCount`	Groups documents by an expression's value and counts them.
`$unionWith`	Combines results from two collections into one. Options available.
`$unset`	Removes specified fields from documents.
`$unwind`	Deconstructs an array field, outputting a document for each element. Options available.

Stages Options

Stage	Option
`$bucket`	`groupBy`: An expression to group by.
	`boundaries`: An array specifying the boundaries to group documents.
	`default`: A literal that specifies the `_id` of an additional group for all documents that do not match any boundary.
`$bucketAuto`	`groupBy`: An expression to group by.
	`buckets`: The number of buckets to create.
`$currentOp`	`allUsers`: A boolean indicating if operations from all users should be returned.
	`localOps`: A boolean indicating if only operations on the local mongod instance should be returned.
`$geoNear`	`near`: The geospatial point to calculate distances from.
	`distanceField`: The field that will contain the calculated distance.
	`spherical`: A boolean specifying whether to treat the `near` point as a sphere.
	`maxDistance`: The maximum distance from the `near` point that the documents can be.
`$graphLookup`	`from`: The target collection for the recursive search.
	`startWith`: The expression that specifies the value of the `connectFromField` with which to start the recursive search.
	`connectFromField`: The field whose value `startWith` references.
	`connectToField`: The field in the documents of the `from` collection that is equal to the `connectFromField`.
	`as`: The array field added to each output document that contains the search results.
`$lookup`	`from`: The target collection.
	`localField`: The field from the input documents.
	`foreignField`: The field from the documents of the `from` collection.
	`as`: The name of the new array field to add to the input documents.
`$merge`	`into`: The target collection.
	`on`: The fields to match on.
	`whenMatched`: The action to take when a matching document exists.
	`whenNotMatched`: The action to take when no matching document exists.
`$out`	`collection`: The target collection.
`$sample`	`size`: The number of documents to randomly select.
`$unionWith`	`coll`: The name of the collection to union with.
	`pipeline`: An optional aggregation pipeline to apply to the specified collection before performing the union.
`$unwind`	`path`: The path to the array field to unwind.
	`includeArrayIndex`: The name of a new field to hold the array index of the element.
	`preserveNullAndEmptyArrays`: A boolean indicating whether to include as an output document those documents that have an empty array or missing array field.

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Transformation Pipeline Expressions

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