猫鼬：$ project中的$ sum仅返回零

Question

我有一个查询，使用$lookup“联接”两个模型，然后使用$project选择我只需要的所有字段，在那个$project中，我需要$sum名为totalValue的值，但仅返回零：

我的查询

User.aggregate([{
      $match: {
        storeKey: req.body.store,
      }
    },
    {
      $group: {
        _id: {
          id: "$_id",
          name: "$name",
          cpf: "$cpf",      
          phone: "$phone",
          email: "$email",
          birthday: "$birthday",
          lastName: "$lastname"      
        },
        totalServices: {
          $sum: "$services"
        },    
      }
    },
    {
      $lookup: {
        from: "schedules",
        "let": { "id": "$_id.phone" },
        "pipeline": [
          { "$match": { "$expr": { "$eq": ["$customer.phone", "$$id"] }}},
          { "$project": { "scheduleStart": 1, "scheduleEnd": 1 }}
        ],
        "as": "user_detail"
      }  
    },  
    {
      $project: {
        _id: 1,
        name: 1,
        name: 1,
        cpf: 1,      
        phone: 1,
        email: 1,
        birthday: 1,
        totalServices: 1,
        totalValue: { $sum : "$user_detail.value" },   // here only return zero   
        count: {
          $sum: 1
        },
        user_detail: 1
      }
    },

Answer 1

您需要在value投影中$project user_details字段中进行下一聚合阶段

{ "$project": { "scheduleStart": 1, "scheduleEnd": 1, "value": 1 }}