Finding and Sorting Records by Date in Mongo with Meteor
A quick tip on Meteor's Mongo sort syntax and why it differs from the raw MongoDB query.
It's a pretty simple thing, but it can trip up beginners — even those with some Mongo experience. I started with Mongo this year, so I'm publishing this tip as a note to myself, since it's hard to find this explained clearly, especially in Portuguese, for newcomers.
I tried running this query in Robo3T:
db.getCollection(‘members’).find({ status: { $eq: true }, birth: { $ne: null} }).sort({ birth: 1 })
It returned what I expected: all active members with a birth date set, sorted ascending (smallest to largest).
However, when I dropped the query into the project:
async birthdays(root, args) {
return MembersCollection.find({ status: { $eq: true }, birth: { $ne: null } }).sort({ birth: 1 }).fetch();
}
It didn't run the query and there was no server-side error — only a client-side one. The function's return value arrived as undefined on the client, and since I was calling data.length to read the size of the birthdays array, the typical JS error kicked in: cannot read property length of undefined.
Meteor ships its own Mongo, with a few methods that differ slightly from MongoDB. To do a sort in Meteor, the syntax must be:
// Sorted by \`createdAt\` descending.
Users.find({}, { sort: { createdAt: -1 } });
And in my project it has to look like this:
async birthdays(root, args) {
return MembersCollection.find({ status: { $eq: true }, birth: { $ne: null } }, { sort: { birth: 1 } }).fetch();
}
A small syntax difference was enough to send me Googling for the fix.
So here's the tip: always check the MongoDB and Meteor docs when you run into trouble with your queries.
References:
https://docs.mongodb.com/manual/reference/method/cursor.sort/
September 4, 2018 · Brazil