Make a mongoDB query using OR statement and array - node.js

Question

I have web interface need to access an URL (shown below) and return only results with requested groups:
http://localhost:3000/device/getgroups/group1,group2,group3,group4
In MongoDB I have entries with the field 'loc_group'.
I want to return the results only where have the field "loc_group" = group1 OR group2 OR group3 OR group4.
My routes are like this:
router.get('/getgroups/:groups', async (req, res) => {
try {
var groups = "req.parms.groups";
#split groups
var arr = groups.split(",");
#iterate in the results on array (arr)
for (var i = 0; i < arr.length; i++) {
arr[i] = ++arr[i];
if (i = arr.lenght) {
var query = "{'loc_group': '" + arr[i] + "' }"
var totals = totals + query;
} else {
var query = "{'loc_group': '" + arr[i] + "' },"
var totals = totals + query;
}
}
# after this for, the totals must looks like
# "{'loc_group': 'group1' }"
# "{'loc_group': 'group2' }"
# "{'loc_group': 'group3' }"
# "{'loc_group': 'group4' }"
#
# then i try to use it on the mongodb query:
const logues = await device.find({ $or: [ totals ], })
res.json(logues)
} catch (err) {
res.status(500).json({ message: err.message })
}
})
but it's not working, what I get when enter the URL is:
{"message":"$or/$and/$nor entries need to be full objects"}
I am a beginner to nodejs and this is my first question here, if need some other information or something please let me know. Thanks.

Answer 1

There are several issues with your code. But the main one is basically ignoring the expectations of API you work with. See, MongoDB expects regular JavaScript objects passed in $or query. What you give it instead is a concatenation of stringified objects, each created by this expression:
var query = "{'loc_group': '" + arr[i] + "' }"
... passed into regular array. Apparently, MongoDB couldn't guess what you wanted, hence $or/$and/$nor entries need to be full objects error.
So, instead of doing JS work on your own, just use native objects to create a query. In fact, you don't even need $or here, as you're looking for the same property's values. Quoting the docs:
When using $or with that are equality checks for the
value of the same field, use the $in operator instead of the $or
operator.
So here's one (simplified) way to do it:
router.get('/getgroups/:groups', async (req, res) => {
const locGroups = req.params.groups.split(',');
const logues = await device.find({ loc_group: { $in: locGroups } });
res.json(logues);
}
What? Yes, that's essentially it. You might consider adding some validation and error handling to this code, and may be some logging, too, but it should be a middleware concern anyway, so the controller stays THAT simple. And that's the beauty - and the reason of existence - of the modern backend-oriented ecosystems: easy things should stay easy.