In mongodb know index of array element matched with $in operator?

Question

I am using aggregation with mongoDB now i am facing a problem here, i am trying to match my documents which are present in my input array by using $in operator. Now i want t

Answer 1

So say we have the following in the database collection:

> db.couponmodel.find()
{ "_id" : "a" }
{ "_id" : "b" }
{ "_id" : "c" }
{ "_id" : "d" }

and we wish to search for the following ids in the collections

var coupons_ids = ["c", "a" ,"z"];

We'll then have to build up a dynamic projection state so that we can project the correct indexes, so we'll have to map each id to its corresponding index

var conditions = coupons_ids.map(function(value, index){
    return { $cond: { if: { $eq: ['$_id', value] }, then: index, else: -1 } };
});

Then we can then inject this in to our aggregation pipeline

db.couponmodel.aggregate([
    { $match : { '_id' : { $in : coupons_ids } } },
    { $project: { indexes : conditions } },
    { $project: {
        index : {
            $filter: { 
                input: "$indexes", as: "indexes", cond: { $ne: [ "$$indexes", -1 ] }
                }
            }
        } 
    },
    { $unwind: '$index' }
]);

Running the above will now output each _id and it's corresponding index within the coupons_ids array

{ "_id" : "a", "index" : 1 }
{ "_id" : "c", "index" : 0 }

However we can also add more items in to the pipeline at the end and reference $index to get the current matched index.

Answer 2

I think you could do it in a faster way simply retrieving the array and search manually. Remember that aggregation don't give you performance.

Answer 3

//$match,$in,$and

    $match:{
        $and:[        
        {"uniqueID":{$in:["CONV0001"]}},
        {"parentID":{$in:["null"]}},
        ]
       }
   }])