我正在尝试创建一个仪表板，在其中显示应用程序内的订单数据摘要。在这种情况下，我只是想计算我的订单集合中给定类别中的项目数。到目前为止，我的代码如下所示:

采集数据

{
    "_id" : "a6wHiXxyM5DwSAsfq",
    "orderNumber" : 1234,
    "createdAt" : "11/01/2016, 14:43:49",
    "productsInOrder" : [
        {
            "category" : "ambient",
            "item" : 50818,
            "desc" : "Tasty Rubber Chicken",
            "quantity" : "44",
            "price" : "0.92",
            "lineprice" : "40.48",
            "_id" : "FFNxG8vujs6NGN69r"
        },
        {
            "category" : "frozen",
            "item" : 71390,
            "desc" : "Generic Granite Fish",
            "quantity" : "11",
            "price" : "1.00",
            "lineprice" : "11.00",
            "_id" : "LcRtpyLxkWyh39kkB"
        }
    ]
}
{
    "_id" : "PdpywXCvfew7qojmA",
    "orderNumber" : 1234,
    "createdAt" : "11/01/2016, 14:44:15",
    "productsInOrder" : [
        {
            "category" : "frozen",
            "item" : 71390,
            "desc" : "Generic Granite Fish",
            "quantity" : "44",
            "price" : "1.00",
            "lineprice" : "44.00",
            "_id" : "dAscx4R8pcBgbzoZs"
        },
        {
            "category" : "frozen",
            "item" : 66940,
            "desc" : "Gorgeous Granite Bike",
            "quantity" : "55",
            "price" : "4.21",
            "lineprice" : "231.55",
            "_id" : "xm3mFRmPmmdPxjfP9"
        },
        {
            "category" : "frozen",
            "item" : 96029,
            "desc" : "Gorgeous Plastic Fish",
            "quantity" : "1234",
            "price" : "4.39",
            "lineprice" : "5417.26",
            "_id" : "7u7SHnpTf7PWcrhGA"
        }
    ]
}
{
    "_id" : "xcHZ25qwvyDpDJtAZ",
    "orderNumber" : 1234,
    "createdAt" : "11/01/2016, 14:44:47",
    "productsInOrder" : [
        {
            "category" : "frozen",
            "item" : 31104,
            "desc" : "Handcrafted Rubber Keyboard",
            "quantity" : "11",
            "price" : "4.78",
            "lineprice" : "52.58",
            "_id" : "LMMwbKFEgnCbgCt9c"
        },
        {
            "category" : "frozen",
            "item" : 77832,
            "desc" : "Practical Rubber Shirt",
            "quantity" : "21",
            "price" : "0.62",
            "lineprice" : "13.02",
            "_id" : "63otkkXWGrTJkwEgX"
        },
        {
            "category" : "frozen",
            "item" : 66940,
            "desc" : "Gorgeous Granite Bike",
            "quantity" : "111",
            "price" : "4.21",
            "lineprice" : "467.31",
            "_id" : "rbPSujey8CFeMPjza"
        }
    ]
}

JS

到目前为止我已经尝试过:

Orders.find({ 'productsInOrder': ['ambient']}).count();
Orders.find({ productsInOrder: { category: 'ambient' }}).count();
Orders.find({ productsInOrder: { $all: [ 'frozen' ] }}).count();

当数据以这种方式嵌套时，我很难理解 Mongo 查询。请你能帮我指出正确的方向吗？非常感谢。

* 解决方案 *

由于以下贡献，我已经取得了预期的结果。为了完成这项工作，我在服务器上创建了一个方法，因为无法使用现有集合在客户端上运行查询。这是按如下方式完成的:

Meteor.methods({
  'byCategory': function() {
    var result = Orders.aggregate([
        { "$unwind": "$productsInOrder" },
        {
            "$group": {
                "_id": null,
                "ambient_count": {
                    "$sum": {
                        "$cond": [ { "$eq": [ "$productsInOrder.category", "ambient" ] }, 1, 0 ]
                    }
                },
                "frozen_count": {
                    "$sum": {
                        "$cond": [ { "$eq": [ "$productsInOrder.category", "frozen" ] }, 1, 0 ]
                    }
                },
                "other_category_count": {
                    "$sum": {
                        "$cond": [ { "$eq": [ "$productsInOrder.category", "other_category" ] }, 1, 0 ]
                    }
                }
            }
        }
    ]);

    return result;
  }
})

然后在客户端:

Meteor.call('byCategory', function( error, result ) {
  if( error ) {
    console.log( error.reason );
  } else {
    console.log( result[0].ambient_count );
    console.log( result[0].frozen_count );
    etc....
  }
});

感谢@chridam 和@Brett。

最佳答案

另一种方法是使用 aggregation framework 。考虑以下聚合管道，它是聚合管道的第一阶段， $unwind 运算符对 productsInOrder 数组进行反规范化以输出每个输入文档，n 文档，其中 n 是数组元素的数量。下一个流水线阶段有 $group 运算符将所有文档分组到一个文档中，并在 $sum 的帮助下存储每个类别的计数。 和 $cond 运营商。

在 Meteor 中，您可以使用 meteorhacks:aggregate package 实现聚合:

meteor add meteorhacks:aggregate

var coll = new Mongo.Collection('orders');
var pipeline = [
    { "$unwind": "$productsInOrder" },
    {
        "$group": {
            "_id": null, 
            "ambient_count": {
                "$sum": {
                    "$cond": [ { "$eq": [ "$productsInOrder.category", "ambient" ] }, 1, 0 ]
                }
            },
            "frozen_count": {
                "$sum": {
                    "$cond": [ { "$eq": [ "$productsInOrder.category", "frozen" ] }, 1, 0 ]
                }
            },
            "other_category_count": {
                "$sum": {
                    "$cond": [ { "$eq": [ "$productsInOrder.category", "other_category" ] }, 1, 0 ]
                }
            }
        }
    }       
];
var result = coll.aggregate(pipeline);

{
    "result" : [ 
        {
            "_id" : null,
            "ambient_count" : 1,
            "frozen_count" : 7,
            "other_category_count" : 0
        }
    ],
    "ok" : 1
}

Meteor.publish('categoryCounts', function() {  
    var self = this,
        db = MongoInternals.defaultRemoteCollectionDriver().mongo.db;

    orders = db.collection("orders").aggregate(pipeline, // Need to wrap the callback so it gets called in a Fiber.
        Meteor.bindEnvironment(
            function(err, result) {
                // Add each of the results to the subscription.
                _.each(result, function(e) {
                    self.added("orders", e._id, e);
                });
                self.ready();
            },
            function(error) {
                Meteor._debug( "Error doing aggregation: " + error);
            }
        )
    );
});

关于javascript - 嵌套对象中的 Meteor Mongodb 计数字段，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/34724545/