MongoDB Map Reduce - Finalize跳过一些结果

Question

我有一个适用于集合的map reduce函数,如下所示:

function Map() {
    emit (
        this.name, 
        { 
            count : 1,
            flag : this.flag

        }
    );
}
function Reduce(key, values) {
    var count = 0;
    var flag = false;

    for (var i in values){
        count = count + 1;
        if (i.flag)
             flag = true;
    }

    var reduced = {
        count : count,
        flag  : flag
    }
    return reduced;
}
function Finalize(key, reduced) {

    if (reduced.count>10 || reduced.flag){
        var finalized = {
            "count" : reduced.count 
        }
        return reduced;
    }

    return null;
}

我想要做的是Finalize只返回通过某个阈值的对象(例如,计数> 10).目前它仍然返回对象,计数只是null.

有任何想法吗？

Answer 1

我建议您使用聚合框架，因为它更快、更容易理解。您的上述 M/R/F 可以简单地写为：

db.so.insert( { name: "Derick" } );
db.so.insert( { name: "Derick" } );
db.so.insert( { name: "Derick" } );
db.so.insert( { name: "Derick" } );
db.so.insert( { name: "Checklist" } );
db.so.insert( { name: "Checklist" } );
db.so.insert( { name: "Whoop" } );
db.so.insert( { name: "Whoop", flagged: true } );
db.so.aggregate( [
    { $group: { 
        _id: '$name', 
        count: { $sum: 1 }, 
        flagged: { $sum: 
            { $cond: [ { $eq: [ '$flagged', true ] }, 1, 0 ] } 
        } 
    } },
    { $match: { $or: [ { count: { $gt: 3 } }, { flagged: { $gt: 0 } } ] } }
] );

返回：

{
    "result" : [
        {
            "_id" : "Whoop",
            "count" : 2,
            "flagged" : 1
        },
        {
            "_id" : "Derick",
            "count" : 4,
            "flagged" : 0
        }
    ],
    "ok" : 1
}