How can I use a regex variable in a query for MongoDB

Question

I would like to make query MongoDB for documents based on a regex expression that I contruct. For e.g I have constructed a simple regex as follows that is a combination of a random letter and a random number for in Nodejs

var randnum = Math.floor((Math.random() * 10) + 1);
var alpha = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','X','Y','Z'];
var randletter = alpha[Math.floor(Math.random() * alpha.length)];
var val = randletter + randnum + '.*;

I have tried various combinations for the regex variable like

var stream = collection.find({"FirstName": /val/).stream();
&&
var stream = collection.find({"FirstName": /$val/).stream();
&&
var stream = collection.find({"FirstName": {$in : [{$regex:val}]}}).stream()
&&
var stream = collection.find({"FirstName": {$in : [{$regex:$val}]}}).stream()

None o it seem to work. However when I write the actual regex I get the records for e.g.

var stream = collection.find({"FirstName": /J.*/).stream();

Any help will be appreciated.

Thanks Ganesh

Wizard, Thanks. However, this did not seem to work.var stream = collection.find({"FirstName": {$regex:val}}).stream(); stream.on("data", function(item) results.push(item); — Tinniam V. Ganesh
– Tinniam V. Ganesh, Commented Nov 2, 2014 at 15:03
Any error occurs, or just doesn't get the expected result? Example of a document stored in the database may be helpful. — Wizard
– Wizard, Commented Nov 2, 2014 at 15:14

Hamza Khan · Accepted Answer · 2018-06-14 07:37:18Z

58

I was having same problem with my title and after lots of searching, i found this answer Here,

var search = 'Joe';
db.users.find(name: /^search/)
db.users.find(name: {$regex: /^search/});
db.users.find(name: {$regex: "/^" + search + "/"});

The queries above won’t return anything. The solution to this little problem is quite simple:

db.users.find(name: new RegExp(search)) //For substring search, case sensitive. 
db.users.find(name: new RegExp('^' + search + '$')) //For exact search, case sensitive
db.users.find(name: new RegExp(search， ‘i')) //For substring search, case insensitive
db.users.find(name: new RegExp('^' +search + '$', 'i')); //For exact search, case insensitive

Other flags or properties can be added base on reference here

answered Jun 14, 2018 at 7:37

Hamza Khan

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5 Comments

rotimi-best Over a year ago

db.users.find(name: {$regex: "/^" + search + "/"}); exactly what I needed

Guilherme Sampaio Over a year ago

For me it didn't work using the /. Like in this example: var name = '.*'+user.name+'.*' found = db.users.findOne({ 'name': {$regex: name} })

Hrishikesh Baidya Over a year ago

i was exactly looking for db.users.find(name: new RegExp('^' +search + '$', 'i')); thanks..

Ajith Over a year ago

Hamza : I am facing an issue with case insensitive and exact search . The rule I have added is as follows {name: new RegExp('^' + search + '$' , "i")} . The prolem is that when I search test... (with dots, which I need since there is entry with dots) , I got results test123, test333 etc.... How can I get only entry test...

Hardik Raval Over a year ago

It's not working with MongoDB. It's passing "search" as a string as supposed to value of the variable.

JohnnyHK · Accepted Answer · 2014-11-02 14:17:41Z

49

You need to create a regular expression object from the string using the RegExp constructor as the /.../ syntax is only for use with literals.

var stream = collection.find({"FirstName": new RegExp(val)}).stream();

answered Nov 2, 2014 at 14:17

JohnnyHK

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3 Comments

Tinniam V. Ganesh Over a year ago

JohnnyHK - That worked awfully well. The changes I made were var val = randletter + ".*" + randnum + ".*"; var stream = collection.find({"FirstName": new RegExp(val)}).stream(); Thanks Ganesh

Avani Khabiya Over a year ago

I have tried what you suggested, but it didn't seem to work. What I have to do is, let pattern = '/^\/'+ cat + '/'; col.find({name: new RegExp(pattern)}) where cat is a variable whose value I am concatenating to create pattern for matching.

JohnnyHK Over a year ago

Remove the / characters from pattern and it will work. @AvaniKhabiya

Murtaza Manasawala · Accepted Answer · 2018-03-30 09:57:04Z

11

Use the following code to use dynamic value in regex with or operations

{$match: { $or: [{ 'title': { $regex:  request.query.val, $options: 'i'} }, { 'skills_required': { $regex:  request.query.val, $options: 'i'} }] }},

answered Mar 30, 2018 at 9:57

Murtaza Manasawala

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1 Comment

aris Over a year ago

$or: [{users: { $elemMatch: { name: { $regex: ${filters.userName}, $options: 'i' } } },}]; . . .. . . .great answer! also works with string interpolation e.g.

Wizard · Accepted Answer · 2014-11-02 14:00:23Z

10

If you want to use the variable val as a parameter of the query part, you can use $regex, for example:

collection.find({"FirstName": {$regex:val}})

It is not allowed to put $regex in $in operator according to the manual.

If you want to put regular expression object in $in operator, you have to use JavaScript regular expression object, for example:

collection.find({"FirstName": {$in: [/abc/, /123/]}})

By the way, val in /val/ is constant string, not the variable as you defined above.

answered Nov 2, 2014 at 14:00

Wizard

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4 Comments

Tinniam V. Ganesh Over a year ago

Hi -Thanks. But it did not work - var val = randletter + randnum + '.*'; var stream = collection.find({"FirstName": {$regex:val}}).stream(); Regards Ganesh

Wizard Over a year ago

@TinniamV.Ganesh, What's value of FirstName in database? Or maybe just no items can satisfy your query needs?

Tinniam V. Ganesh Over a year ago

Wizard - Firstname is just a string of letters and numbers. I tried it a couple of times it always returned an empty set. The other version var stream = collection.find({"FirstName": new RegExp(val)}).stream(); worked. Thanks anyway. Regards Ganesh

Wizard Over a year ago

@TinniamV.Ganesh, Thanks for the reply. I think I missed some details about your circumstances which do not support $regex.

Scott Wager · Accepted Answer · 2021-01-27 16:00:44Z

8

If your regex includes a variable, make sure to escape it.

function escapeRegExp(string) {
  return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'); // $& means the whole matched string
}

This can be used like this

new RegExp(escapeRegExp(searchString), 'i')

Or in a mongoDb query like this

{ '$regex': escapeRegExp(searchString) }

Posted same comment here

answered Jan 27, 2021 at 16:00

Scott Wager

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Chukwuemeka Maduekwe · Accepted Answer · 2022-03-26 23:05:42Z

3

let test = `what your regex should search`;

collection.find({
    fieldName: {$regex: test}
}).then(result => red.send(result));

// tested on mongoose but should work on mongodb too

edited Mar 26, 2022 at 23:05

answered Jan 25, 2020 at 17:53

Chukwuemeka Maduekwe

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Comments

Hardik Raval · Accepted Answer · 2022-03-31 04:55:46Z

0

My use case was to fetch results STARTS WITH a given query, and below solution worked for me.

let q = '^' + query;
return await User.find({ name: { $regex: q, $options: 'i' } }).select('name').limit(10);

answered Mar 31, 2022 at 4:55

Hardik Raval

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