How to check $setDifference in two array using mongo-query

问题

UserDetails

{
    "_id" : "5c23536f807caa1bec00e79b",
    "UID" : "1",
    "name" : "A",
},
{
    "_id" : "5c23536f807caa1bec00e78b",
    "UID" : "2",
    "name" : "B",
}

UserProducts

{
    "_id" : "5c23536f807caa1bec00e79c",
    "UPID" : "100",
    "UID" : "1"
},
{
    "_id" : "5c23536f807caa1bec00e79c",
    "UPID" : "200",
    "UID" : "2"
}

Groups

{
    "_id" : "5bb20d7556db6915846da55f",
    "members" : {
        "regularStudent" : [
            "200" // UPID
        ],
    }
}

Step 1

I have to take UID from UserDetails check with UserProducts then take UPID from UserProducts

Step 2

we have to check this UPID mapped to Groups collection or not ?. members.regularStudent we are mapped UPID

Step 3

Suppose UPID not mapped means i want to print the UPID from from UserProducts

I have tried but couldn't complete this, kindly help me out on this.

Expected Output:

["100"]

Note: Expected Output is ["100"] , because UserProducts having UPID 100 & 200 but Groups collection mapped only 200.

My Code

db.UserDetails.aggregate(
{
$lookup: {
    from: "UserProducts",
    localField: "UID",
    foreignField: "UID",
    as: "userProduct"
    }
},
{ $unwind: "$userProduct" },
{
    "$project": { "_id" : 0, "userProduct.UPID" : 1 }
},
{
    $group: {
        _id: null,
        userProductUPIDs: { $addToSet: "$userProduct.UPID" }
    }
}
) // returns [ "100", "200" ]

db.Groups.aggregate([
    {
        $unwind: "$members.regularStudent"
    },
    {
        $group: {
            _id: null,
            UPIDs: { $addToSet: "$members.regularStudent" }
        }
    }
]) // returns ["200"]

Now i want to check $setDifference of both array, so i had added below code but returning error like $userProductUPIDs is not defined

  db.Groups.aggregate([
    {
        $unwind: "$members.regularStudent"
    },
    {
        $group: {
            _id: null,
            UPIDs: { $addToSet: "$members.regularStudent" }
        }
    },
    {
        $project: {
            members: {
                $setDifference: [ $userProductUPIDs , "$members" ]
            },
            _id : 0
        }
    }
    ])

回答1:

As this is a follow up to one of my previous answers I will try to fix your code. The bottom line is that you need two queries as you can't upgrade your database so the code should look like below:

var queryResult = db.UserDetails.aggregate(
{
$lookup: {
    from: "UserProducts",
    localField: "UID",
    foreignField: "UID",
    as: "userProduct"
    }
},
{ $unwind: "$userProduct" },
{
    "$project": { "_id" : 0, "userProduct.UPID" : 1 }
},
{
    $group: {
        _id: null,
        userProductUPIDs: { $addToSet: "$userProduct.UPID" }
    }
});

let userProductUPIDs = queryResult.toArray()[0].userProductUPIDs;

db.Groups.aggregate([
    {
        $unwind: "$members.regularStudent"
    },
    {
        $group: {
            _id: null,
            UPIDs: { $addToSet: "$members.regularStudent" }
        }
    },
    {
        $project: {
            members: {
                $setDifference: [ userProductUPIDs , "$UPIDs" ]
            },
            _id : 0
        }
    }
]) // should return 100

来源：https://stackoverflow.com/questions/54128386/how-to-check-setdifference-in-two-array-using-mongo-query

标签

mongodb

mongodb-query

aggregation-framework

aggregate