Question

我有这个文件

并且只想提取{ "_id" : ObjectId("6afda532e9a0e3838537c71a"), "VersionId" : 0, "NodeId" : [ { "NodeId" : 0, "Host" : "127.0.0.1", "DatabaseName" : "NodeId0", "Collection" : [ { "CollectionId" : 0, "CollectionName" : "Codice0" }, { "CollectionId" : 1, "CollectionName" : "Codice1" } ] }, { "NodeId" : 1, "Host" : "127.0.0.2", "DatabaseName" : "NodeId1", "Collection" : [ { "CollectionId" : 1, "CollectionName" : "Codice1" } ] } ] }的1个字段和nodeId的1个字段，是否可能？

返回的文档应具有以下结构：

CollectionId

我尝试了这个查询，没有结果：

{
    VersionId: 0,
    NodeId: {
        NodeId: 0,
        Collection: {
          CollectionId: 0,
          CollectionName: Codice0
        }
    }
}

Answer 1

如果您使用＆＃34; VersionId＆＃34;或者使用_Id然后结果如下：

db.getCollection('a').aggregate([
{$unwind: '$NodeId'},
{$unwind: '$NodeId.Collection'},
{$match: {"_id" : ObjectId("5846b47c8254f4cad9acadce"), "VersionId" : 0, "NodeId.NodeId": 0, "NodeId.Collection.CollectionId": 0}}
])

输出如下数据：

{
    "_id" : ObjectId("5846b47c8254f4cad9acadce"),
    "VersionId" : 0,
    "NodeId" : {
        "NodeId" : 0,
        "Host" : "127.0.0.1",
        "DatabaseName" : "NodeId0",
        "Collection" : {
            "CollectionId" : 0,
            "CollectionName" : "Codice0"
        }
    }
}

Answer 2

您可以尝试以下内容。利用 $map 投影所需字段，并使用 $filter 进行过滤匹配Node和Collection以及 $arrayElemAt ，将数组更改为object以匹配预期的输出格式。

aggregate([{
    $match: {
        "VersionId": 0
    }
}, {
    $project: {
        NodeId: {
            $arrayElemAt: [{
                $map: {
                    input: {
                        $filter: {
                            input: "$NodeId",
                            as: "prova",
                            cond: {
                                $eq: ["$$prova.NodeId", 0]
                            }
                        }
                    },
                    as: "nd",
                    in: {
                        "NodeId": "$$nd.NodeId",
                        "Collection": {
                            $arrayElemAt: [{
                                $filter: {
                                    input: "$$nd.Collection",
                                    as: "proval",
                                    cond: {
                                        $eq: ["$$proval.CollectionId", 0]
                                    }
                                }
                            }, 0]
                        }
                    }
                }
            }, 0]
        },
        _id: 0
    }
}])

MongoDB查询中的多个过滤器

2 个答案: