如何用聚合芒果的相同goods_info.name减去2个子文档

Question

我试图用相同的goods_in和goods_out减去goods_info.name。我试过了，还在坚持，请帮帮我

[
    {
        "_id": "5f1aaa902f90f940a40546fe",
        "goods_in": [
            {
                "goods_info": {
                    "name": "taro"
                },
                "quantity": 100
            },
            {
                "goods_info": {
                    "name": "granita"
                },
                "quantity": 17
            }
        ],
        "goods_out": [
            {
                "goods_info": {
                    "name": "taro"
                },
                "quantity": 25
            },
            {
                "goods_info": {
                    "name": "taro"
                },
                "quantity": 15
            },
        ]
    }
]

期望产出：

[{"name":"taro","quantity":60},{"name":"granita","quantity":17}]

有什么帮助吗。我试过小组等

Answer 1

您可以使用此聚合，如果goods_ids可以在多个文档之间存在重复，则必须添加一个$group阶段，否则就会得到dup结果。

db.collection.aggregate([
  {
    $unwind: "$goods_in"
  },
  {
    $project: {
      name: "$name",
      quantity: {
        $subtract: [
          "$goods_in.quantity",
          {
            $sum: {
              $map: {
                input: {
                  $filter: {
                    input: "$goods_out",
                    as: "good",
                    cond: {
                      $eq: [
                        "$$good.goods_info.name",
                        "$goods_in.goods_info.name"
                      ]
                    }
                  }
                },
                as: "item",
                in: "$$item.quantity"
              }
            }
          }
        ]
      }
    }
  }
])

MongoPlayground

Answer 2

通过aggregation和group，您可以处理它，通过组阶段您可以在out_value变量中推入out数量之和，然后在lookup同名的字段上用第一个集合加入结果。在聚合结束时，您可以减去in_value和out_value。

db.collection.aggregate(
    [
        {
            "$unwind": "$goods_out"
        },
        {
            "$group": {
                "$_id": "goods_out.name", "out_value": {"$sum": "good_out.quantity"}
            }
        },
        {
            "$lookup": {
                "from": "collection_name",
                "let": {"name": "$_id", "out_value": "$out_value", "in_value": "$goods_in.quantity"},
            "pipeline": [
                {
                  "$unwind": "$goods_in"
                },
                {
                    "$match": {

                    "$expr":
                        {"$eq": ["$$goods_in.name", "$_id"]}
                }}
            ],
            "as": "goods_info"
            }
        },
        {
            "$unwind": "$goods_info"
        },
        {
            "$project":{
                "name": "$goods_info.name",
                "quantity": {
                    "$subtract": ["$goods_info.in_value", "$goods_info.in_value"]
                }
            }
        }

    ]
)