Mongodb递归查询 [英] Mongodb recursive query

问题描述

我的taxon集合中具有以下架构:

I have the following schema in my taxon collection :

{ 
  "_id": 1, 
  "na": [ "root_1",
        "root_2",
        "root_3" ], 
  "pa": 1 
},{
  "_id": 2, 
  "na": [ "name_1", 
        "name_2", 
        "name_3"], 
  "pa": 1
},{
  "_id": 4, 
  "na": [ "otherName_1", 
        "otherName_2", 
        "otherName_3"],
  "pa": 2
}

每个文档都通过父字段与另一个文档相关，该字段对应于其父文档的 _id .

Each document is related to another by the parent field, which correspond to the _id of it's parent.

我想执行递归搜索以得到以下结果:

I would like to perform a recursive search to get the following result:

{ "_id": 4, 
  "nameList": [ "otherName_1",
              "name_1",
              "root_1"]
} 

从具有特定 _id 的文档中，获取每个父级的 na 数组的第一项，直到到达具有_id: 1的文档

我目前通过执行X个查询(例如，按父文档一个，这里为3个)来获得此结果，但是我很确定可以使用单个查询来实现.我已经查看了新的 $ graphLookup 运算符，但无法设法解决它...

I currently get this result by performing X queries (one by parent document, here 3 for example), but I'm pretty sure that this can be achieved using a single query. I already looked at the new $graphLookup operator, but couldn't manage to get my way with it...

是否可以使用MongoDB 3.4.1在单个查询中实现?

Is it possible to achieve this in a single query using MongoDB 3.4.1?

修改

我每次都要运行50个文档，因此最佳的解决方案是将所有内容合并到一个查询中

I would run this for 50 documents each time, so the optimal solution would be to combine everything in a single query

例如，它看起来像

var listId = [ 4, 128, 553, 2728, ...];
var cursor = db.taxon.aggregate([
  {$match: 
     { _id: {$in: listId}}
  }, ...
)];  

并输出:

[{ "_id": 4, 
  "nameList": [ "otherName_1",
              "name_1",
              "root_1"]
}, { "_id": 128, 
  "nameList": [ "some_other_ame_1",
              "some_name_1",
              "root_1"]
}, { "_id": 553, 
  "nameList": [ "last_other_ame_1",
              "last_name_1",
              "root_1"]
} ... ]

在线试用: mongoplayground.net/p/Gfp-L03Ub0Y

推荐答案

您可以尝试以下聚合.

You can try below aggregation.

阶段$match - $graphLookup - $project.

$reduce从每个$graphLookup nameList's na数组中选择第一个元素.

$reduce to pick the first element from the each of $graphLookup nameList's na array.

db.taxon.aggregate([{
    $match: {
        _id: {
            $in: listId
        }
    }
}, {
    $graphLookup: {
        from: "taxon",
        startWith: "$_id",
        connectFromField: "pa",
        connectToField: "_id",
        as: "nameList"
    }
}, {
    $project: {
        nameList: {
            $reduce: {
                input: "$nameList",
                initialValue: [],
                in: {
                    "$concatArrays": ["$$value", {
                        $slice: ["$$this.na", 1]
                    }]
                }
            }
        }
    }
}])

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