如何使用 MongoDB 递归查询树结构?

问题描述

例如树结构为;

[{id: 1 , childrenIdList: [2, 3]},{id: 2 , childrenIdList: [4, 5]},{id: 3 , childrenIdList: []},{id: 4 , childrenIdList: [6, 7]},{id: 5 , childrenIdList: []},{id: 6 , childrenIdList: []},{id: 7 , childrenIdList: []}]

就像;

 12 34 56 7

如何从叶子节点(id=7)到根节点(id=1)追踪树?

找到id=7的父节点很容易；

db.document.find({childrenList: { $in: [7]}}, {id: 1}).toArray(function(err), result{/*结果给出{"id" : NumberInt(4)}现在我应该看看 id=4 的父级和 id=2 的父级，正如你所知.*/})

在 mongodb 上可以进行递归查询吗?我该如何实施?

解决方案

根据您的用例，MongoDB v3.4 提供了一个 聚合管道 操作符，称为 $graphLookup.聚合运算符能够对集合执行递归搜索.查看关于 $graphLookup 定义的更多定义.

使用上面的文档层次结构和值作为示例，您可以尝试在聚合下运行:

db.collectionName.aggregate([{$放松:{路径:"$childrenIdList",preserveNullAndEmptyArrays: true}},{$graphLookup:{来自:集合名称"，startWith:"$_id",connectFromField:"_id",connectToField:"childrenIdList",如:我的父母"，限制搜索匹配:{"_id"}}},{$match: {"_id": 7 } },{$组:{_id:"$_id",父母:{$addToSet:"$myparents._id"}}}]);

以上应该返回如下结果:

{ "_id" : 7, "parents" : [ [ 1, 2, 4 ] ] }

话虽如此，如果你有一个大集合，上面的查询可能性能不佳，因为你将执行 $unwind 并且无法使用索引.正如其他人所建议的，您应该重新考虑您的文档模型结构.请参阅数据模型树结构.根据您的应用程序逻辑和查询用例进行优化，让灵活的文档架构跟随.

For example a tree structure as;

[
    {id: 1 , childrenIdList: [2, 3]},
    {id: 2 , childrenIdList: [4, 5]},
    {id: 3 , childrenIdList: []},
    {id: 4 , childrenIdList: [6, 7]},
    {id: 5 , childrenIdList: []},
    {id: 6 , childrenIdList: []},
    {id: 7 , childrenIdList: []}
]

which is like;

               1
          2        3
       4    5
    6    7

How can I trace tree from starting the leaf node(id=7) to root(id=1)?

Finding the parent of id=7 is easy as;

db.document.find({childrenList: { $in: [7]}}, {id: 1}).toArray(function(err), result{
  /*result gives
  {"id" : NumberInt(4)}
  now I should look the parent of id=4, and parent of id=2 as you know.
  */
})

Is recursive queries possible on mongodb? How can I implement it?

解决方案

Depending on your use case, MongoDB v3.4 provides an aggregation pipeline operator called $graphLookup. The aggregation operator is able to perform a recursive search on a collection. See more definiton on $graphLookup definition.

Using your documents hierarchy and values above as examples, you could try running below aggregation:

db.collectionName.aggregate([

                {$unwind:{
                        path:"$childrenIdList",
                        preserveNullAndEmptyArrays: true}
                  },
                {$graphLookup:{
                        from:"collectionName",
                        startWith:"$_id",
                        connectFromField:"_id",
                        connectToField:"childrenIdList",
                        as:"myparents",
                        restrictSearchWithMatch: {"_id"}}
                  },
                {$match: {"_id": 7 } },
                {$group:{
                        _id:"$_id",
                        parents:{$addToSet:"$myparents._id"}
                  }}
]);

The above should return result as below:

{ "_id" : 7, "parents" : [ [ 1, 2, 4 ] ] }

Having said that, if you have a large collection the above query may not be performant as you'll be performing $unwind on each documents and won't be able to utilise indexes. As suggested by others, you should re-consider your document model structure. See Data Models Tree Structures. Optimise based on your application logic and querying use case, and let the flexible document schema follow.

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