具有猫鼬聚合和求和嵌套字段的节点

Question

当我对 collection...

执行此查询时

models.Project.find(function(err, result) {
    //result = doc below
}).populate('media')

...我得到这个结果：

{ 
  _id: 57f36baa6cf34d079c8474a0,
  code: 'ZMIA',
  __v: 0,
  media:[
    { 
      _id: 57f36bb26cf34d079c847766,
      project_code: 'ZMIA',
      amount: 228,
      __v: 0 
    },
    { 
      _id: 57f36bb26cf34d079c84775c,
      project_code: 'ZMIA',
      amount: 250,
      __v: 0 
    } 
  ]
},
{ 
  _id: 57f36baa6cf34d079c8474a1,
  code: 'ZMJU',
  __v: 0,
  media: [] 
}

media 是一个参考字段。如何将嵌套媒体 objects（如果存在）聚合到 $sum amount 字段并将结果按 project_code 分组？

Answer 1

您可以使用聚合框架，其中运行聚合管道由扁平文档上的初始 $unwind pipeline that will denormalize the media field since it is an array and then a $lookup operator to do a left join to the collection that has the media refs. A further $unwind operator is needed to flatten the array field produced as a result of the join and then do a $group 运算符管道组成，以生成期望的结果。

运行以下管道应该适合您：

models.Project.aggregate([
    { "$unwind": "$media" },
    {
        "$lookup": {
            "from": "media", // <-- collection to join
            "localField": "media",
            "foreignField": "_id",
            "as": "media_joined"
        }
    },
    { "$unwind": "$media_joined" },
    {
        "$group": {
            "_id": "$media_joined.project_code",
            "total": { "$sum": "$media_joined.amount" }
        }
    }
], function(err, result){
    console.log(result);
})

具有猫鼬聚合和求和嵌套字段的节点

Node with mongoose aggregate and sum nested fields

mongoose

mongodb

node.js

aggregation-framework

mongodb-aggregation