mongodb中的聚合嵌套数组元素本身

Question

是否可以在Mongodb中聚合嵌套数组元素本身？例如原始数据是

{"transId" : "12345","customer" : "cust1", "product" : [{"type" : "cloth","price" : 100},{"type" : "toy","price" : 200}]}
{"transId" : "45672","customer" : "cust1", "product" : [{"type" : "cloth","price" : 10},{"type" : "toy","price" : 500}]}
{"transId" : "99999","customer" : "cust2", "product" : [{"type" : "cloth","price" : 40},{"type" : "toy","price" : 5}]}

我希望每个嵌套数组元素都根据客户的类型进行聚合。

结果

{"customer" : "cust1", "product" : [{"type" : "cloth","price" : 110},{"type" : "toy","price" : 700}]}
{"customer" : "cust2", "product" : [{"type" : "cloth","price" : 40},{"type" : "toy","price" : 5}]}

你能帮我示范一下怎么做吗？谢谢。

Answer 1

您可以使用聚合框架来完成这个任务。您需要使用$unwind操作对"product“数组进行去denormalize。从那里你需要两个$group阶段。在第一个组阶段，您按照_id (在您的情况下必须是一个复合字段)对文档进行分组，并使用$sum累加器操作符返回价格之和。在最后一个$group阶段，您使用$push累加器操作符返回一个"product“数组。

db.customers.aggregate([ 
    // Denormalize the product array
    { "$unwind": "$product" }, 
    // Group your documents by `_id`
    { "$group": { 
        "_id": { "customer": "$customer", "type": "$product.type" }, 
        "price": { "$sum": "$product.price" } 
    }}, 
    // reconstruct the "product" array.
    { "$group": { 
        "_id": "$_id.customer", 
        "product": { "$push": { "type": "$_id.type", "price": "$price" } } 
    }}
])

返回：

{
        "_id" : "cust1",
        "product" : [
                {
                        "type" : "toy",
                        "price" : 700
                },
                {
                        "type" : "cloth",
                        "price" : 110
                }
        ]
}
{
        "_id" : "cust2",
        "product" : [
                {
                        "type" : "toy",
                        "price" : 5
                },
                {
                        "type" : "cloth",
                        "price" : 40
                }
        ]
}