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

Answer 1

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();