MongoDB query $in with regex array of element

Using $in can be fairly efficient with small arrays but not so well with huge lists since it will skip around in the index to find the matching documents, or walk through the whole collection if there isn't an index to use.

Besides using the $in with the regular expression, you could use a pipe-delimited regex pattern with the keywords list like this:

Test documents:

db.papertest.insert([
    { category: "ad bd cd" },
    { category: "dd ed fd" },
    { category: "gd hd id" },
    { category: "jd kd ld" },
    { category: "md nd od" },
    { category: "pd qd rd" },
    { category: "sd td ud" },
    { category: "vd wd xd yd zd" },
]);

The magic:

var keywords = ["xd", "sd", "ad"],
    regex = keywords.join("|");

db.papertest.find({
    "category": {
        "$regex": regex, 
        "$options": "i"
    } 
});

The results

{ "_id" : ObjectId("56bb6f171bb4f693057c0ba4"), "category" : "ad bd cd" }
{ "_id" : ObjectId("56bb6f171bb4f693057c0baa"), "category" : "sd td ud" }
{ "_id" : ObjectId("56bb6f171bb4f693057c0bab"), "category" : "vd wd xd yd zd" }

it does not work when the double quotes are present because they are interpreted as strings instead of as RegExp objects. So to make it to work, you have to convert it to RegExp objects first in Javascript like this.

var sea = [ "xd", "sd", "ad" ]; // Note: no slashes
var regex = [];
for (var i = 0; i < sea.length; i++) {
    regex[i] = new RegExp(sea[i]);
}
db.paper.find({"category": {$in: regex}});

Remember, MongoDB shell uses Javascript

It seems to be working fine for me please try this

var sea = [ "xd", "sd", "ad" ];

var regex = sea.map( function( val ){ 
        return new RegExp( '^['+val+'].*','i' ); 
    }) 

db.paper.find({"category": { $in: regex }});

For this you can add a regular expression to each item in the array, you can do it in the following way.

data = ['hoLA','Que','TAL', 'Nueva'];
data  = data.map(function(v, i){return new RegExp(v, 'i')});
MyCollection.find({"thing": {$in : data}}, function(err, data){
    if (err) {
        console.log(err)
    }else{
        data.forEach(function(item){
            console.log(item.nombre);
        })
    }
});

Slightly improved ES6 + TypeScript answer based on Meme Composer comment:

const sea: string[] = [ "xd", "sd", "ad" ];
const regex: RegExp[] = sea.map((value) => new RegExp(value));

db.paper.find({ "category": { $in: regex } });

Here is simple way to transform /.*/ style regex.

var sea = [ "/xd/", "/sd/", "/ad/" ];

var rx = [];
sea.forEach(function name(value) {
    var v = value.replace(/\//ig,"");
    rx.push(new RegExp(v));
});

db.paper.find({"category": {$in: rx}});