pez Posts - Convex Community

pez

•Created by pez on 3/21/2025 in #support-community

Fetching a random subset of documents without having to collect() over the entire set?

Hi team, I'm implementing an app where a core user flow is to be able to answer a subset of questions from a collection of documents I have stored in Convex. Right now, I have it implemented in a way where I fetch ALL of the documents (this can bloat to thousands eventually), and then apply filters related to which questions I'd like to exclude, and then return only a random subset of these documents. This makes my db bandwidth usage skyrocket over time and I'd really like to optimize this. Is there any simpler way to get a random subset of docs from Convex? If not, is there a more efficient way of implementing this in general? I've attached a code snippet below.

export const getRandomQuestions = query({
  args: {
    quantity: v.number(),
    exclusionIds: v.optional(v.array(v.id("templateQuestions"))),
  },
  handler: async (ctx, args) => {
    const { exclusionIds, quantity } = args;

    const questions = await ctx.db.query("templateQuestions").collect();
    const filteredQuestions = exclusionIds
      ? questions.filter((q) => !exclusionIds.includes(q._id))
      : questions;

    // Use current timestamp as seed for reproducible randomness within same millisecond
    const seed = Date.now();
    const random = mulberry32(seed);
    for (let i = filteredQuestions.length - 1; i > 0; i--) {
      const j = Math.floor(random() * (i + 1));

      // Modern swap syntax
      [filteredQuestions[i], filteredQuestions[j]] = [
        filteredQuestions[j],
        filteredQuestions[i],
      ];
    }

    return filteredQuestions.slice(0, quantity);
  },
});

export const getRandomQuestions = query({
  args: {
    quantity: v.number(),
    exclusionIds: v.optional(v.array(v.id("templateQuestions"))),
  },
  handler: async (ctx, args) => {
    const { exclusionIds, quantity } = args;

    const questions = await ctx.db.query("templateQuestions").collect();
    const filteredQuestions = exclusionIds
      ? questions.filter((q) => !exclusionIds.includes(q._id))
      : questions;

    // Use current timestamp as seed for reproducible randomness within same millisecond
    const seed = Date.now();
    const random = mulberry32(seed);
    for (let i = filteredQuestions.length - 1; i > 0; i--) {
      const j = Math.floor(random() * (i + 1));

      // Modern swap syntax
      [filteredQuestions[i], filteredQuestions[j]] = [
        filteredQuestions[j],
        filteredQuestions[i],
      ];
    }

    return filteredQuestions.slice(0, quantity);
  },
});

40 replies

CCConvex Community

•Created by pez on 3/18/2025 in #support-community

Tips on sending batch notifications to a large group of users at once?

Hi team, for context - I'm storing user ExpoPushTokens in my users table in Convex. I was reading some of the docs on cron jobs in Convex and was wondering what the recommended approach would be to send daily notifications to a large group of users at once (doesn't have to be at exactly the same time). I was thinking I could make a call to fetch the users table (though I'd probably wanna do this in a paginated manner so I don't fetch too many items at once), get the Expo push tokens that way, and then make batched calls to the Expo service using an internal action. Is this the recommended approach for a use case like this?

13 replies

CCConvex Community

•Created by pez on 3/10/2025 in #support-community

Unable to access identity from ctx.auth.getUserIdentity in HTTP action

Hi team, I'm trying to secure my image upload HTTP action and currently call the action via a hook. I'm using Clerk for auth and was able to confirm that calling useAuth() then awaiting the getToken function returns a JWT token. When I pass this token in as an Authorization header to my call to my HTTP action and then call ctx.auth.getUserIdentity() within the action, I keep seeing null. Any ideas what may be going on here? Thanks!

3 replies

CCConvex Community

•Created by pez on 2/24/2025 in #support-community

SMS auth with Convex

Hi guys, building out an Expo RN app and I have it all setup with Clerk right now for SMS authentication. Saw Clerk's pricing based on MAUs and was wondering if Convex Auth priced similarly. My main way of authenticating users right now would be based on SMS verification codes (but will likely also support Google/Apple down the line). I know the Convex team recommends third-party auth solutions but does anyone has experience using Convex Auth in a prod app? Would love to hear from the community!

4 replies