unable to use regex in $in operator in mongodb

Question

I am trying to use the regex with $in operator as mentioned in the docs but I am still unable to get the value.

db.users.find({'profile.firstName':{$in:["/justin/i"]}}).count() = 0

but when I used like this

db.users.find({'profile.firstName':{$in:["justin"]}}).count()=1 and

db.users.find({'profile.firstName':{$in:["Justin"]}}).count()=2

Edited Question

seems like I am not clear with the question I will add the code for easy understanding

I am trying to get the list of documents from a query which is case insensitive.I think it better to explain my doubt with code.

Meteor.users.find({'profile.firstName':{$in:[/justin/i,/helen/i]}}).count()

will give documents whose profile.firstName is justin/Justin/JUSTIn/HElen/helen

but my doubt how to give the variable x=["sai","test","jacob",---etc] in place of helen/justin

Answer 1

You need to wrap the elements in the array with the RegExp object i.e.

regex = [new RegExp("sai", "i"), new RegExp("test", "i"),...]

You can use the map() method to map the elements in the array with the RegExp wrappers to a new array that you can then use in the regex query with $in:

var x = ["sai","test","jacob","justin"],
    regex = x.map(function (e) { return new RegExp(e, "i"); });

db.users.find({"profile.firstName": { "$in": regex } });

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:

var x = ["sai","test","jacob","justin"],
    regex = x.join("|");

db.users.find({
    "profile.firstName": {
        "$regex": regex, 
        "$options": "i"
    } 
}).count;

Answer 2

try doing this way

db.users.find({'profile.firstName':{$in:[/justin/i]}}).count() = 0

you are passing regex as string.

Usually You should ask one problem at a time so question remains focused to a specific problem

well You can directly pass it, like this

// Here I am creating regex for all the elements in array
let myRegex = new RegExp(myArray.join('|'), i) 
and then I can pass this regex
db.users.find({'profile.firstName':{$in: myRegex}}).count() = 0