[SOLVED] Find random entry without fetching entire mongo cursor

react
1

My goal is to fetch a random entry in my collection, one entry at a time.

Here is my current code,

const randomentry = useTracker(() => myCollection.find({}, {limit: 1, skip: Math.floor(Math.random() * 30000 }).fetch());

this fetch all my data (30000 entries…, and than jump to a random entry. which is highly unefficient.

My data is structured like this:
[{id: “randomstringbits”, text: “entry text”}, […]}

I wish i would set find({id: randomint}) where randomint is < than mycollection.find({]).count() but the id is non predictable and non ordered. and also fetching all my data just to know its size is highly unefficient.

Is there a way to fetch one entry at a time using a minimongo operator within the first argument? Or any other way?

2
3

Use a auto increment value on a key so you have numbers going from 1 to 30000 or whatever your count limit is

Then just pick a random value 1 - Max and select by that key on a findOne, add a index to the key and cache the result. CPU will 100% idle.

let max         = 30000; //Could hold a hourly count here from db and cache it if its a growing dataset
let randomIndex = Math.floor(Math.random() * max);
let result      = myCollection.findOne({index: randomIndex});

As a rule of thumb for good design - Never do random or any functions at database, use your scripting language for it and at most only ever do a sort on an indexed key, but try to avoid if possible and leverage the power of your scripting language. Picking a random number in node is effortless, doing so at database is not.

4

Collection.aggregate is not implemented in Meteor as far I know.

5
6

{index: randomnumber} is not a key that exists in my data.
My index (_id) is a random hex string.
Your answer is telling to rewrite my data, which is what i want to avoid for now.

7

As I said, there is not aggregate Method in Collections Documentation.
You are inviting me to use $sample which only work in aggregate method, which doesn’t exist.
Screenshot from 2022-03-04 19-32-58-1

As you can you see in the documentation caption, Aggregate is not a Meteor function.

8

Collection.rawCollection() - read it

9

Thank you but there is only one line and not much of explanations.

Screenshot from 2022-03-04 19-40-08

I’ll try to figure it out somehow see if it can be used to call aggregate method.

10
11

Thanks rjdavid, here is the working code for my problem:


async function getRandomEntry(collection) { 
  return await collection.rawCollection().aggregate(
  [{ 
    $sample: { size: 1 }
  }] 
).toArray()
}
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