How to convert request query to correct MongoDB query string?

Question

The request (req.query) I got has this format:

{ duration: { gte: '5' }, difficulty: 'easy' }

To make it work in MongoDB, the final result should be as below

{ duration: { $gte: 5 }, difficulty: 'easy' }

This is the code I'm using

const queryObj = { ...req.query };
let queryStr = JSON.stringify(queryObj);
queryStr = queryStr.replace(/\b(gte|lte|gt|lt)\b/g, (match) => `$${match}`);

However, the output is { duration: { '$gte': '5' }, difficulty: 'easy' } so it didn't work.

{ duration: { $gte: 5 }, difficulty: 'easy' } : return every matched records
{ duration: { '$gte': '5' }, difficulty: 'easy' }: return 0 record.

My question is: How can i remove the '' sign so it can be used for query string?

Tom Slabbaert · Accepted Answer · 2020-05-06 06:30:07Z

1

The regex approach won't work with converting numbers as a regex is binding you to stay with string. You're going to have to iterate over the entire object and check each key.

Here is a very simple recursive function that achieves this:

let finalObject = { duration: { gte: '5' }, difficulty: 'easy' }

function recursivelySearchObject(object) {
    if (typeof object === "string") {
        if (/^\d+$/.test(object)) {
            return parseInt(object)
        } else {
            return object
        }
    } else {
        Object.keys(object).forEach((key) => {
            object[key] = recursivelySearchObject(object[key]);
        });
        return object
    }
}

recursivelySearchObject(finalObject);

You can skip the recursive aspect if the object will always be "shallow" and just check to a certain depth using a for loop instead.

answered May 6, 2020 at 6:30

Tom Slabbaert

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5 Comments

The One Over a year ago

Thank you, it worked! By the way, I'm still puzzled at why the query string with ' ' didn't work. Is this expected?

Tom Slabbaert Over a year ago

I'm not sure what you mean by query string but Mongo expects a number for $gte. it doesn't validate and sanitize input.

The One Over a year ago

I edited my question with a bit more information. Basically, I tried 2 different query string in Mongo DB Atlas filter.

Tom Slabbaert Over a year ago

So the problem is again with the 5, Mongo can receive key names without " or ' around them as-long as you're not using the dot notation, but as i mentioned $gte expects a number in this context. otherwise is trying to compare strings and your field is not string type.

The One Over a year ago

Ah I see!! Thank you, Tom.

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