mongodb从另一个json对象中的json对象进行搜索

好了:

db.collection.aggregate({
    $addFields: {
        "friends": {
            $arrayToObject: { // transform the array of key-value pairs back into a subdocument
                $filter: {
                    input: {
                        $objectToArray: "$friends" // transform the "friends" subdocument into an array of key-value pairs
                    },
                    as: "this",
                    cond: {
                        $eq: [ "$$this.v.name", "Y" ] // we only want the ones where the name is "Y"
                    }
                }
            }
        }
    }
})