如何对Mongo Db聚合框架的输出应用过滤器？

本文介绍了如何对Mongo Db聚合框架的输出应用过滤器？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我正在尝试为Mongo Db聚合的输出应用条件，但仍然不知道这个想法。这是我的示例文档：

I'm trying to apply condition for the output of the aggregation of Mongo Db but still do not figure out the idea. Here are my sample documents:

{ 'id':1, 'customerReviews':[5,7,8], 'expertReviews':[9,8,9] }, { 'id':1, 'customerReview':[6,7,7], 'expertReview':[4,8,9] }

因此，如果我有一个要求，例如查找所有具有min（customer_review）> 5->的文档，则仅第二个文档是正确的。

So if I have a requirement like find all documents which has min(customer_review) > 5 -> only the second document is correct.

这是我获得文档的min（customerReview）的初始要点：

Here is my initial point which get the min(customerReview) of documents:

db.getCollection('subscriber').aggregate([ {$unwind:"$customerReviews"}, {"$group":{ "_id":"$_id", "min_customer_review":{"$min":"$customerReviews"}}} ]);

会产生：

{ "_id" : ObjectId("58ab1d6892bf3194a9719883"), "min_customer_review" : 5 }, { "_id" : ObjectId("58ab1d6892bf3194a9719883"), "min_customer_review" : 6 }

那么如何继续对聚合输出应用过滤器，以获取具有min_customer_review> 5的所有文档？

So how to continue apply filter for aggregation output to get all documents which has min_customer_review > 5?

还有一个问题，它是否可以应用第二个聚合，例如全部获取影片的min_customer_review> 5或average_expert_reviews> 6？

One more question, is it able to apply second aggregation, like "get all movies which has min_customer_review > 5 or average_expert_reviews > 6" ?

谢谢大家

推荐答案

您可以使用 $ redact 。

$ redact 浏览文档并根据查询条件执行 $$ KEEP 和 $$ PRUNE 。

$redact to go through document and perform $$KEEP and $$PRUNE on the query criteria.

db.subscriber.aggregate( [{ $redact: { $cond: { if: { $gt: [{ $min: "$customerReviews" }, 5] }, then: "$$KEEP", else: "$$PRUNE" } } }] );

您可以在 $ or 中包装更多条件

You can wrap more conditions in $or operator.

将 if 块中的值替换为

{ $or:[{$gt: [{ $min: "$customerReviews"}, 5 ] }, {$gt: [{ $avg: "$expertReviews"}, 6 ] } ]}