Node.js Mongodb查找聚合未获取所有字段值

我有两个类似于模式的集合

driver

_id:5f9c1d897ea5e246945cd73a
agent_name:"Ratnabh Kumar Rai"
agent_email:"ra2614@gmail.com"
agent_phone:"70****63331"

及

因此，我想计算平均驾驶员等级。我尝试使用查找聚合，以便获得所有详细信息，然后再计算总和…我所做的是

let doc = await db
        .collection("drivers")
        .aggregate([
        
          {
            $project: {
              _id: {
                $toString: "$_id",
              },
            },
          },
          {
            $lookup: {
              from: "reviews",
              localField: "_id",
              foreignField: "driver_id",
              as: "driver_info",
            },
          },
          {
            $project: {
              agent_email: 1,
              orderReview: "$driver_info",
            },
          },
        ])
        .toArray();

但我得到的结果是

 {
    _id: '5f9d63eb8737e82fbc193dd9',
     orderReview: [ [Object], [Object], [Object], [Object], [Object] ]
   }

---

这部分是正确的，因为我还需要从我的localfield集合（即drivers field）中获取详细信息，到目前为止，您可以看到我在投影中只获取驱动程序的id，我也做了“代理电子邮件：1”，但没有获取电子邮件，您实际上只在第一个管道中投影了id，因此只有id被传递到其他管道，如果你需要在更多的管道中发送电子邮件，你也需要将其投射出来

    let doc = await db.collection("drivers").aggregate([
  {
    $project: {
      _id: {
        $toString: "$_id",
        
      },
      agent_email: "$agent_email"
    },
    
  },
  {
    $lookup: {
      from: "reviews",
      localField: "_id",
      foreignField: "driver_id",
      as: "driver_info",
      
    },
    
  },
  {
    $project: {
      agent_email: 1,
      orderReview: "$driver_info",
      
    },
    
  },
  
])

MongoDB游乐场：

[更新]

我意识到你这样做是为了得到平均值，如果你需要在一个聚合查询中得到平均值，这里是你如何做到的

使用“展开”操作符，可以将reviews数组展平为对象，然后按_id分组并使用$avg聚合操作符

db.collection("drivers").aggregate([
  {
    $project: {
      _id: {
        $toString: "$_id",
        
      },
      agent_email: "$agent_email"
    },
    
  },
  {
    $lookup: {
      from: "reviews",
      localField: "_id",
      foreignField: "driver_id",
      as: "driver_info",
      
    },
    
  },
  // Makes the driver info flat with other information
  {
    "$unwind": "$driver_info"
  },
  {
    // Now you can group them 
    $group: {
      _id: "$_id",
      // Calculates avg on rating field
      avg: {
        "$avg": "$driver_info.rating"
      },
      // To make email field appear in next pipeline.
      // You can do it for other fields too like Name, etc
      agent_email: {
        $first: "$agent_email"
      }
    }
  },
  {
    $project: {
      // select the fields you want to display
      agent_email: 1,
      avg: 1
    },
    
  },
  
])

db.collection("drivers").aggregate([
  {
    $project: {
      _id: {
        $toString: "$_id",
        
      },
      agent_email: "$agent_email"
    },
    
  },
  {
    $lookup: {
      from: "reviews",
      localField: "_id",
      foreignField: "driver_id",
      as: "driver_info",
      
    },
    
  },
  // Makes the driver info flat with other information
  {
    "$unwind": "$driver_info"
  },
  {
    // Now you can group them 
    $group: {
      _id: "$_id",
      // Calculates avg on rating field
      avg: {
        "$avg": "$driver_info.rating"
      },
      // To make email field appear in next pipeline.
      // You can do it for other fields too like Name, etc
      agent_email: {
        $first: "$agent_email"
      }
    }
  },
  {
    $project: {
      // select the fields you want to display
      agent_email: 1,
      avg: 1
    },
    
  },
  
])