使用 mongodb 获得条件总和

Question

我需要通过idCategory 获得销售总额，知道吗？ 我在 mongondb 中有这 3 个模式

category = [{"id":1,"name":"cat1"}, {"id":2,"name":"cat2"}]
product  = [{"id":1,"name":"product1", "catId":1}, {"id":2,"name":"product2", "catId":2}]
sells    = [{"id":1,"value":80, "productId":1, status:'active'},  {"id":2,"value":90, "productId":2, status:'Inactive'}]  

Answer 1

MongoDB 集合也不是实际的模式，我假设：

• 您将它们解释为数组（尽管它们不是），因此您的意思是您的每个集合中都有 2 个文档。

• 您想要按产品类别分组的销售额总和。

如果是这种情况，您需要的是一个 MongoDB Aggregate，您可以在“sells”集合上运行，“join”与“product”集合并按类别 ID 分组。

这样做的基本聚合将遵循以下几行：

sells.aggregate([
    {
        $lookup: {
            from: "product",
            localField: "productId",
            foreignField: "id",
            as: "ProductData"
        }
    },
    {
        $unwind: "$ProductData"
    },
    {
        $group: {
            _id: "$ProductData.catId",
            total: { $sum: "$value" }
        }
    }
]);

如果您还想在聚合后获取类别名称，您只需在与类别集合连接的管道末尾插入另一个 $lookup：

sells.aggregate([
    {
        $lookup: {
            from: "product",
            localField: "productId",
            foreignField: "id",
            as: "ProductData"
        }
    },
    {
        $unwind: "$ProductData"
    },
    {
        $group: {
            _id: "$ProductData.catId",
            total: { $sum: "$value" }
        }
    },
    {
        $lookup: {
            from: "category",
            localField: "_id",
            foreignField: "id",
            as: "CategoryData"
        }
    },
    { 
        $unwind: "$CategoryData"
    },
    {
        $project: {
            name: "$CategoryData.name",
            total: 1
        }
    }
]);

编辑（在评论中添加新案例请求）：

db.getCollection('product').aggregate([
    {
        $lookup: {
            from: "sells",
            localField: "id",
            foreignField: "productId",
            as: "SalesData"
        }
    },
    {
        $unwind:
        {
            path: "$SalesData",
            preserveNullAndEmptyArrays: true
        }
    },
    {
        $project: {
            catId: 1,
            value: "$SalesData.value"
        }
    },
    {
        $group: {
            _id: "$catId",
            total: { $sum: "$value" }
        }
    },
    {
        $lookup: {
            from: "category",
            localField: "_id",
            foreignField: "id",
            as: "CategoryData"
        }
    },
    { 
        $unwind: "$CategoryData"
    },
    {
        $project: {
            name: "$CategoryData.name",
            total: 1
        }
    }
]);