Question

第一个文档：

    {
    "_id" : 1,
    "array" : [ 
        {
            "userID" : 1,
            "name" : "name 1"
        }, 
        {
            "userID" : 2,
            "name" : "name 2"
        }, 
        {
            "userID" : 3,
            "name" : "name 3"
        }, 
        {
            "userID" : 6,
            "name" : "name 6"
        }
    ]
}

第二个文档：

    {
    "_id" : 2,
    "array" : [ 
        {
            "userID" : 1,
            "name" : "name 1"
        }, 
        {
            "userID" : 2,
            "name" : "name 2"
        }, 
        {
            "userID" : 3,
            "name" : "name 3"
        }, 
        {
            "userID" : 4,
            "name" : "name 4"
        }, 
        {
            "userID" : 5,
            "name" : "name 5"
        }
    ]
}

有什么办法可以得到这样的输出：

   {    
    "array" : [  
        {  
            "userID" : 1,  
            "name" : "name 1" 
        },  
        {  
            "userID" : 2,  
            "name" : "name 2"  
        },   
        {  
            "userID" : 3,  
            "name" : "name 3"  
        }  
    ]  

    }

我想比较两个文档的数组字段并检索其中的公共元素。并仅通过公用'userID'比较数组字段。我们可以通过$setIntersection来做到吗？我一次只需要检查两个数组字段。

Answer 1

您可以使用$setIntersection

db.t67.aggregate([
    //{$match : {}} add filter criteria to filter documents
    {$group : {_id : null, array : {$push : "$array"}}},
    {$project : {_id :0, array : {$reduce : {input : "$array", initialValue : {$arrayElemAt : ["$array", 0]}, in : {$setIntersection : ["$$this", "$$value"]}}}}}
])

输出

> db.t67.aggregate([
...     {$group : {_id : null, array : {$push : "$array"}}},
... {$project : {_id :0, array : {$reduce : {input : "$array", initialValue : {$arrayElemAt : ["$array", 0]}, in : {$setIntersection : ["$$this", "$$value"]}}}}}
... ])
{ "array" : [ { "userID" : 1, "name" : "name 1" }, { "userID" : 2, "name" : "name 2" }, { "userID" : 3, "name" : "name 3" } ] }

或$unwind和$group

db.t67.aggregate([
    // $match stages to filter 2 documents
    {$unwind : "$array"},
    {$group : {_id : "$array", count : {$sum : 1}}},
    {$match : {count : {$gt : 1}}},
    {$project : {count : 0}},
    {$group : {_id : null, array : {$push : "$_id"}}},
    {$project : {_id : 0}}
])

输出

{ "_id" : null, "array" : [ { "userID" : 3, "name" : "name 3" }, { "userID" : 2, "name" : "name 2" }, { "userID" : 1, "name" : "name 1" } ] }

如何获取常见的数组元素mongodb

1 个答案: