Question

当我们从集合“Articles”

中获取数据时，MongoDB返回以下JSON数组

[{
    "_id": "id1",
    "description": "Description for article",
    "author": "publisher of article"
}, {
    "_id": "id2",
    "description": "Description for article",
    "author": "publisher of article"
}, {
    "_id": "id3",
    "description": "Description for article",
    "author": "publisher of article"
}]

但是我希望json采用以下格式

[{
    "id1": {
        "_id": "id1",
        "description": "Description for article",
        "author": "publisher of article"
    },
    "id2": {
        "_id": "id2",
        "description": "Description for article",
        "author": "publisher of article"
    },
    "id3": {
        "_id": "id3",
        "description": "Description for article",
        "author": "publisher of article"
    }
}]

是否可以使用MongoDB查询获得此类结果？

Answer 1

您可以使用map reduce执行此操作：

地图功能：

var mapFunction = function() {
    var obj = {};

    obj[this._id] = {

        "_id": this._id,
        "description": this.description,
        "author": this.author

    };
    emit(1,obj);
};

减少功能：

var reduceFunction = function(key, values) {

    var reduced = {};

    var output_arr = [];

    values.forEach(function(value) {
        Object.keys(value).forEach(function(key) {
            var obj = {};
            obj[key]=value[key];
            output_arr.push(obj);
        });
    });

    reduced["data"] = output_arr;

    return reduced;

};

地图缩减查询：

db.items.mapReduce(mapFunction, reduceFunction, { out: { inline: 1 } })

您可以在results[0].value.data中访问结果。输出是：

{
    "results" : [
        {
            "_id" : 1,
            "value" : {
                "data" : [
                    {
                        "id1" : {
                            "_id" : "id1",
                            "description" : "Description for article",
                            "author" : "publisher of article"
                        }
                    },
                    {
                        "id2" : {
                            "_id" : "id2",
                            "description" : "Description for article",
                            "author" : "publisher of article"
                        }
                    },
                    {
                        "id3" : {
                            "_id" : "id3",
                            "description" : "Description for article",
                            "author" : "publisher of article"
                        }
                    }
                ]
            }
        }
    ],
    "timeMillis" : 11,
    "counts" : {
        "input" : 3,
        "emit" : 3,
        "reduce" : 1,
        "output" : 1
    },
    "ok" : 1
}

格式化MongoDB结果

1 个答案: