$addFields | Adds new fields to documents. Similar to $project, $addFields reshapes each document in the stream; specifically, by adding new fields to output documents that contain both the existing fields from the input documents and the newly added fields.向文档中添加新字段。与$project类似，$addFields会重塑流中的每个文档；具体来说，通过向输出文档添加新字段，这些字段既包含输入文档中的现有字段，也包含新添加的字段。
$set is an alias for $addFields.是$addFields的别名。 |
$bucket | Categorizes incoming documents into groups, called buckets, based on a specified expression and bucket boundaries.根据指定的表达式和桶边界将传入文档分类到称为桶的组中。 |
$bucketAuto | Categorizes incoming documents into a specific number of groups, called buckets, based on a specified expression. 根据指定的表达式将传入文档分类到特定数量的组中，称为桶。Bucket boundaries are automatically determined in an attempt to evenly distribute the documents into the specified number of buckets.桶边界是自动确定的，试图将文档均匀地分布到指定数量的桶中。 |
$changeStream | Returns a Change Stream cursor for the collection. This stage can only occur once in an aggregation pipeline and it must occur as the first stage.返回集合的“更改流”游标。此阶段在聚合管道中只能发生一次，并且必须作为第一阶段发生。 |
$changeStreamSplitLargeEvent | Splits large change stream events that exceed 16 MB into smaller fragments returned in a change stream cursor.将超过16MB的大型更改流事件拆分为更改流游标中返回的较小片段。
You can only use $changeStreamSplitLargeEvent in a $changeStream pipeline and it must be the final stage in the pipeline.您只能在$changeStream管道中使用$changeStreamSplitRateEvent，并且它必须是管道中的最后一个阶段。 |
$collStats | Returns statistics regarding a collection or view.返回有关集合或视图的统计信息。 |
$count | Returns a count of the number of documents at this stage of the aggregation pipeline.返回聚合管道此阶段的文档数量计数。
Distinct from the $count aggregation accumulator.不同于$count聚合累加器。 |
$densify | Creates new documents in a sequence of documents where certain values in a field are missing.在字段中缺少某些值的文档序列中创建新文档。 |
$documents | Returns literal documents from input expressions.从输入表达式返回文本文档。 |
$facet | Processes multiple aggregation pipelines within a single stage on the same set of input documents. 在同一组输入文档的单个阶段内处理多个聚合管道。Enables the creation of multi-faceted aggregations capable of characterizing data across multiple dimensions, or facets, in a single stage.允许创建能够在单个阶段跨多个维度或方面表征数据的多面聚合。 |
$fill | Populates null and missing field values within documents.填充文档中的null字段值和缺失的字段值。 |
$geoNear | Returns an ordered stream of documents based on the proximity to a geospatial point. 根据与地理空间点的接近程度返回有序的文档流。Incorporates the functionality of $match, $sort, and $limit for geospatial data. 结合了地理空间数据的$match、$sort和$limit功能。The output documents include an additional distance field and can include a location identifier field.输出文档包括附加的距离字段，并且可以包括位置标识符字段。 |
$graphLookup | Performs a recursive search on a collection. To each output document, adds a new array field that contains the traversal results of the recursive search for that document.对集合执行递归搜索。向每个输出文档添加一个新的数组字段，其中包含该文档的递归搜索的遍历结果。 |
$group | Groups input documents by a specified identifier expression and applies the accumulator expression(s), if specified, to each group. 按指定的标识符表达式对输入文档进行分组，并将累加器表达式（如果指定）应用于每个组。Consumes all input documents and outputs one document per each distinct group. The output documents only contain the identifier field and, if specified, accumulated fields.消耗所有输入文档，并为每个不同的组输出一个文档。输出文档仅包含标识符字段和累积字段（如果指定）。 |
$indexStats | Returns statistics regarding the use of each index for the collection.返回有关集合中每个索引使用情况的统计信息。 |
$limit | Passes the first n documents unmodified to the pipeline where n is the specified limit. 将前n个文档原封不动地传递给管道，其中n是指定的限制。For each input document, outputs either one document (for the first n documents) or zero documents (after the first n documents).对于每个输入文档，输出一个文档（对于前n个文档）或零个文档（在前n个文件之后）。 |
$listClusterCatalog | Retrieves information for collections in a cluster, including names and creation options.检索群集中集合的信息，包括名称和创建选项。 |
$listSampledQueries | Lists sampled queries for all collections or a specific collection.列出所有集合或特定集合的采样查询。 |
$listSearchIndexes | Returns information about existing MongoDB Search indexes on a specified collection or view.返回指定集合或视图上现有MongoDB搜索索引的信息。 |
$listSessions | Lists all sessions that have been active long enough to propagate to the system.sessions collection.列出所有已激活足够长时间以传播到system.sessions集合的会话。 |
$lookup | Performs a left outer join to another collection or view in the same database to filter in documents from the "joined" collection or view for processing.对同一数据库中的另一个集合或视图执行左外联接，以从“联接”的集合或视图中筛选文档进行处理。 |
$match | Filters the document stream to allow only matching documents to pass unmodified into the next pipeline stage. 筛选文档流，只允许匹配的文档未经修改地传递到下一个管道阶段。$match uses standard MongoDB queries. For each input document, outputs either one document (a match) or zero documents (no match).使用标准的MongoDB查询。对于每个输入文档，输出一个文档（匹配）或零个文档（不匹配）。 |
$merge | Writes the resulting documents of the aggregation pipeline to a collection. The stage can incorporate (insert new documents, merge documents, replace documents, keep existing documents, fail the operation, process documents with a custom update pipeline) the results into an output collection. 将聚合管道的结果文档写入集合。该阶段可以将结果合并（插入新文档、合并文档、替换文档、保留现有文档、操作失败、使用自定义更新管道处理文档）到输出集合中。To use the $merge stage, it must be the last stage in the pipeline.要使用$merge阶段，它必须是管道中的最后一个阶段。 |
$out | Writes the resulting documents of the aggregation pipeline to a collection. 将聚合管道的结果文档写入集合。To use the $out stage, it must be the last stage in the pipeline.要使用$out阶段，它必须是管道中的最后一个阶段。 |
$planCacheStats | Returns plan cache information for a collection.返回集合的计划缓存信息。 |
$project | Reshapes each document in the stream, such as by adding new fields or removing existing fields. For each input document, outputs one document.重新整形流中的每个文档，例如添加新字段或删除现有字段。对于每个输入文档，输出一个文档。
See also $unset for removing existing fields.另请参阅$unset以删除现有字段。 |
$querySettings | Returns query settings previously added with setQuerySettings.返回以前使用setQuerySettings添加的查询设置。
New in version 8.0.在版本8.0中新增。 |
$queryStats | Returns runtime statistics for recorded queries.返回已记录查询的运行时统计信息。
WARNING:警告： The $queryStats aggregation stage is unsupported and is not guaranteed to be stable in a future release. Don't build functionality that relies on a specific output format of this stage, since the output may change in a future release.$queryStats聚合阶段不受支持，也不能保证在未来的版本中稳定。不要构建依赖于此阶段特定输出格式的功能，因为输出可能会在未来的版本中发生变化。
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$rankFusion | Combines the results of input pipelines that rank documents. 组合对文档进行排序的输入管道的结果。$rankFusion de-duplicates input pipeline results and uses the Reciprocal Rank Fusion algorithm to create a final document ranking.$rankFusion消除输入管道结果的重复，并使用往复式排名融合算法创建最终文档排名。 |
$redact | Reshapes each document in the stream by restricting the content for each document based on information stored in the documents themselves. Incorporates the functionality of $project and $match. 根据文档本身存储的信息限制每个文档的内容，从而对流中的每个文档进行重新整形。结合了$project和$match的功能。Can be used to implement field level redaction. For each input document, outputs either one or zero documents.可用于实现字段级编校。对于每个输入文档，输出一个或零个文档。 |
$replaceRoot | Replaces a document with the specified embedded document. The operation replaces all existing fields in the input document, including the _id field. 用指定的嵌入文档替换文档。该操作将替换输入文档中的所有现有字段，包括_id字段。Specify a document embedded in the input document to promote the embedded document to the top level.指定嵌入在输入文档中的文档，以将嵌入的文档提升到顶层。
$replaceWith is an alias for $replaceRoot stage.是$replaceRoot阶段的别名。 |
$replaceWith | Replaces a document with the specified embedded document. The operation replaces all existing fields in the input document, including the _id field. Specify a document embedded in the input document to promote the embedded document to the top level.用指定的嵌入文档替换文档。该操作将替换输入文档中的所有现有字段，包括_id字段。指定嵌入在输入文档中的文档，以将嵌入的文档提升到顶层。
$replaceWith is an alias for $replaceRoot stage.$replaceWith是$replaceRoot阶段的别名。 |
$sample | Randomly selects the specified number of documents from its input.从输入中随机选择指定数量的文档。 |
$search | Performs a full-text search of the field or fields in an Atlas collection.对Atlas集合中的一个或多个字段执行全文搜索。
To learn more, see MongoDB Search Aggregation Pipeline Stages.要了解更多信息，请参阅MongoDB搜索聚合管道阶段。 |
$searchMeta | Returns different types of metadata result documents for the MongoDB Search query against an Atlas collection. 返回针对Atlas集合的MongoDB搜索查询的不同类型的元数据结果文档。To learn more, see MongoDB Search Aggregation Pipeline Stages.要了解更多信息，请参阅MongoDB搜索聚合管道阶段。 |
$set | Adds new fields to documents. Similar to $project, $set reshapes each document in the stream; specifically, by adding new fields to output documents that contain both the existing fields from the input documents and the newly added fields.向文档中添加新字段。与$project类似，$set对流中的每个文档进行重新整形；具体来说，通过向输出文档添加新字段，这些字段既包含输入文档中的现有字段，也包含新添加的字段。<
$set is an alias for $addFields stage.$set是$addFields阶段的别名。 |
$setWindowFields | Groups documents into windows and applies one or more operators to the documents in each window.将文档分组到窗口中，并对每个窗口中的文档应用一个或多个运算符。
New in version 5.0.在版本5.0中新增。 |
$skip | Skips the first n documents where n is the specified skip number and passes the remaining documents unmodified to the pipeline. For each input document, outputs either zero documents (for the first n documents) or one document (if after the first n documents).跳过前n个文档，其中n是指定的跳过数，并将其余文档原封不动地传递给管道。对于每个输入文档，输出零个文档（对于前n个文档）或一个文档（如果在前n个文件之后）。 |
$sort | Reorders the document stream by a specified sort key. Only the order changes; the documents remain unmodified. For each input document, outputs one document.按指定的排序键重新排序文档流。只有顺序发生了变化；文档保持不变。对于每个输入文档，输出一个文档。 |
$sortByCount | Groups incoming documents based on the value of a specified expression, then computes the count of documents in each distinct group.根据指定表达式的值对传入文档进行分组，然后计算每个不同组中的文档计数。 |
$unionWith | Performs a union of two collections; i.e. combines pipeline results from two collections or views into a single result set.执行两个集合的并集；即，将来自两个集合或视图的管道结果组合到一个结果集中。 |
$unset | Removes/excludes fields from documents.从文档中删除/排除字段。
$unset is an alias for $project stage that removes fields.$unset是删除字段的$project阶段的别名。 |
$unwind | Deconstructs an array field from the input documents to output a document for each element. 从输入文档中解构数组字段，为每个元素输出一个文档。Each output document replaces the array with an element value. For each input document, outputs n documents where n is the number of array elements and can be zero for an empty array.每个输出文档都用元素值替换数组。对于每个输入文档，输出n个文档，其中n是数组元素的数量，对于空数组可以为零。 |
$vectorSearch | Performs an ANN or ENN search on a vector in the specified field of an Atlas collection.在Atlas集合的指定字段中对向量执行ANN或ENN搜索。
$vectorSearch is only available for MongoDB Atlas clusters running MongoDB v6.0.11 or higher, and is not available for self-managed deployments.$vectorSearch仅适用于运行MongoDB v6.0.11或更高版本的MongoDB Atlas集群，不适用于自我管理部署。<
New in version 7.0.2.在版本7.0.2中新增。
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