Fork聚合管道 [英] Fork the pipeline of aggregation

问题描述

我同时有几个类似的聚合操作，例如

I have several similar aggregation operations at the same time, for example

db.cases.aggregate([
   {$match : query},
   {$unwind : "factors"},

   //operation 1 of the above result
   // ...
])

db.cases.aggregate([
   {$match : query},
   {$unwind : "factors"},

   //operation 2 of the above result
   // ...
])

聚合的前两个阶段( $match, $unwind )是一样的，我认为重复重复的阶段是一种浪费.所以我在问是否有一种方法可以分叉管道，以便它可以共享前两个阶段的结果，如下所示，

The first two stages of aggregation( $match, $unwind ) are the same, and I think it would be a waste to repeat the duplicate stages. So I am asking if there exists a way to forking the pipeline, so that it can share the result from the first two stages, as follows,

db.cases.aggregation([
   {$match : query},
   {$unwind : "factors"},
   forks : [
      {... operation 1},
      {... operation 2}
   ]
])

推荐答案

这是很久以前的事了，但你知道它已经实施了:

This was a while ago but just so you know it was implemented:

https://docs.mongodb.com/manual/reference/运算符/聚合/方面/

{ $facet:
   {
      <outputField1>: [ <stage1>, <stage2>, ... ],
      <outputField2>: [ <stage1>, <stage2>, ... ],
      ...

   }
}

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