检索使用其他查询更改了字段值的文档 [英] Retrieve document with fields' value changed using another query

问题描述

我在该国的MongoDB上有该数据库，其中包含OpenStreetMap的数据，我使用 Node- Mongosm 并生成三个集合:nodes，ways和relations.

I have this database on MongoDB for my country with data of OpenStreetMap, I imported it with Node-Mongosm and produces three collections: nodes, ways and relations.

请求Way时，将输出以下文档(从mongo shell):

When requesting a Way, the following document is output (from mongo shell):

{
   "_id":492464922,
   "tags":{
      "maxspeed":"20",
      "surface":"asphalt",
      "highway":"residential",
      "oneway":"yes",
      "name":"Avenida 1"
   },
   "loc":{
      "type":"Polygon",
      "coordinates":[

      ],
      "nodes":[
         445848963,
         4844871065,
         432568566
      ]
   }
}

字段coordinates为空是出于我未知的原因(不确定这是Node-Mongosm的功能还是bug)，但是我可以填充该字段，并从nodes字段中检索每个节点的坐标，即:节点445848963:

The field coordinates is empty for reasons unknown to me (not sure if this is a feature or a bug from Node-Mongosm), but I can populate it retrieving the coordinates of each node from the nodes field, i.e.: node 445848963:

{
   "_id":445848963,
   "loc":{
      "type":"Point",
      "coordinates":[
         -83.5047254,
         10.0984515
      ]
   }
}

所以，我的问题是，是否可能以及如何编写查询，该查询用于从ways集合中收集具有节点节点(ways.loc.nodes字段)动态地协调 ，因此检索到的文档看起来像这样:

So, my question is if it is possible and how should I write the query for gathering a document from ways collection with the field coordinates populated with the nodes' (ways.loc.nodes field) coordinates on the fly so the retrieved document looks like this:

{
   "_id":492464922,
   "tags":{
      "maxspeed":"20",
      "surface":"asphalt",
      "highway":"residential",
      "oneway":"yes",
      "name":"Avenida 1"
   },
   "loc":{
      "type":"Polygon",
      "coordinates":[
         -83.5047254,
         10.0984515,
         -83.5052237,
         10.0987132,
         -83.5056339,
         10.0989286
      ],
      "nodes":[
         445848963,
         4844871065,
         432568566
      ]
   }
}

推荐答案

您可以使用聚合管道

db.ways.aggregate(
[
    {$lookup : {
        from : "coords",
        localField : "loc.nodes",
        foreignField : "_id",
        as : "loc.coordinates"
    }},
    {$addFields : {
            "loc.coordinates" : {
                $reduce : {
                  input : "$loc.coordinates.loc.coordinates", 
                  initialValue :[], 
                  in : { $concatArrays : ["$$this", "$$value"] }
                }
            }
        }
    }
]
).pretty()

结果

{
    "_id" : 492464922,
    "tags" : {
        "maxspeed" : "20",
        "surface" : "asphalt",
        "highway" : "residential",
        "oneway" : "yes",
        "name" : "Avenida 1"
    },
    "loc" : {
        "type" : "Polygon",
        "coordinates" : [
            -83.5047254,
            10.0984515
        ],
        "nodes" : [
            445848963,
            4844871065,
            432568566
        ]
    }
}

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