如何对Mongo Db聚合框架的输出应用过滤器？ [英] How to apply filter for output of aggregation framework of Mongo Db?

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 ] } ]}

这篇关于如何对Mongo Db聚合框架的输出应用过滤器？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！