lookup with add extra field in mongodb

Question

My OBJ

[{
_id:XXXXXXXXXX,
role:admin
},
{
_id:XXXXXXXXXX,
role:superUser
}]

and need results using aggregation how to solve this using aggregation

[{
name:'username'
role:'test'
}

]

Answer 1

I suppose you need the following

let db1 = db.get().collection(`temp1`);
    let db2 = db.get().collection(`temp2`);

    await db1.aggregate([
        {
            $lookup: {
                from: "temp2",
                localField: "_id",    // field in the orders collection
                foreignField: "_id",  // field in the items collection
                as: "users"
            }
        },
        {
            $replaceRoot: { newRoot: { $mergeObjects: [{ $arrayElemAt: ["$users", 0] }, "$$ROOT"] } }
        },
        { $project: { users: 0 } }
    ]).toArray()