如何将结果汇总并合并到集合中? [英] How to aggregate and merge the result into a collection?

问题描述

我想聚合结果并将其插入到现有集合中，而不删除该集合.该文档似乎暗示这不是直接可能的.我很难相信.

I want to aggregate and insert the results into an existing collection, without deleting that collection. The documentation seems to suggest that this isn't directly possible. I find that hard to believe.

map-reduce功能具有输出模式"，包括合并"，它可以实现我想要的功能.我正在寻找聚合的等效项.

The map-reduce functionality has 'output modes', including 'merge', which does what I want. I'm looking for the equivalent for aggregation.

新的 $out 聚合阶段支持插入到集合，但它代替了集合而不是对其进行了更新.如果这样做，我将不得不运行另一个map-reduce将其合并到另一个集合中，这似乎效率很低.

The new $out aggregation stage supports inserting into a collection, but it replaces the collection rather than updating it. If I did this I would (I think) have to run another map-reduce to merge this into another collection, which seems inefficient.

我是否缺少某些功能，或者只是聚合功能中缺少该功能?

Am I missing something or is the functionality just missing from the aggregation feature?

推荐答案

我使用了聚合的输出来插入/合并到集合:

I used the output from aggregation to insert/merge to collection:

    db.coll2.insert(
      db.coll1.aggregate([]).toArray()
    )

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