How to apply filter for output of aggregation framework of Mongo Db?

问题

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]
}

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

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"}}}
]);

which produces:

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

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

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" ?

Thank u all

回答1:

You can use $redact.

$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"
            }
        }
    }]
);

You can wrap more conditions in $or operator.

Replace the value in if block with

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

来源：https://stackoverflow.com/questions/42351601/how-to-apply-filter-for-output-of-aggregation-framework-of-mongo-db

标签

mongodb

aggregation-framework