MongoDB - How to use JavaScript variable in expression?

Question

How do you put a variable inside this expression? I tried

var myVariable = 'something';

db.test.find({$where: "myVariable.match( ... )"});

but I get an error "myVariable is not defined". What's the way to do this?

I tried what you have just posted. Didn't get any error. Can you elaborate more? — dikesh
– dikesh, Commented Apr 20, 2015 at 5:45
If you want to do this you will need to use $eval to put the variable in the scope of the function — Sammaye
– Sammaye, Commented Apr 20, 2015 at 7:41
Note: use of $where is generally discouraged as JavaScript evaluation cannot take advantage of indexes. If you can include an example of a sample document and actual query you're trying to construct, there is likely a more performant alternative to recommend. — Stennie
– Stennie, Commented Apr 20, 2015 at 8:34
@stennie I'm not sure there is. {$where: "myVariable.match(new RegExp(this.test + '$'))"}. If myVariable = 'something', it should get documents that match the end substring, e.g., mething, thing, ing. — Sunny
– Sunny, Commented Apr 20, 2015 at 8:58

Sede · Accepted Answer · 2015-04-20 06:39:19Z

2

You need your variable to be in the local scoop of $where like this:

db.test.find({ "$where": function(){
    var myVariable = "something";
    return myVariable.match( ... )
    }
);

answered Apr 20, 2015 at 6:39

Sede

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