Dynamic queries in MongoDB and Node.js

Question

I am working on a nodejs/express app with Mongodb on the backend. In one of my API calls, depending on the presence of a particular querystring parameter or the other I want to issue a query to Mongodb with either a $gt or a $lt.

In some cases we want to ask for everything less than the tokenId using $lt, but in other cases we want everything greater than the tokenId using $gt. How do we do that without duplicating the queries?

Here's an example query:

collection.find({'film_id': {$in : genre}, '_id': {$lt: tokenId}}).sort({'_id': -1}).limit(25).toArray(function(error, films)

Is there a way to dynamically create the query without actually doing 2 different queries?

JohnnyHK · Accepted Answer · 2016-01-28 14:06:04Z

17

Build up your query object programmatically:

var query = {'film_id': {$in : genre}};
if (param) {
    query._id = {$lt: tokenId};
} else {
    query._id = {$gt: tokenId};
}
collection.find(query).sort({'_id': -1}).limit(25).toArray(function(error, films);

Update

Now that Node.js 4+ supports computed property names, you can create query in one step as:

var query = {
    film_id: {$in: genre},
    _id: {[param ? '$lt' : '$gt']: tokenId}
};

edited Jan 28, 2016 at 14:06

answered Dec 1, 2012 at 17:13

JohnnyHK

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Comments

jHilscher · Accepted Answer · 2016-01-26 21:03:24Z

0

The Above code may not work. The above dynamic query will be resolved to following Ex. Token is an integer 35.

collection.find("_id":"{$gt: 35}")
          .sort({'_id': -1}).limit(25).toArray(function(error, films);

resulting in Error

The correct syntax should be:

collection.find("_id":{$gt: 35}).

The double "" quotes should not be there.

edited Jan 26, 2016 at 21:03

jHilscher

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answered Jan 26, 2016 at 20:15

sharad sinha

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1 Comment

Richard Erickson Over a year ago

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