BillzabobB
Convex Community•10mo ago•
2 replies
Billzabob

Paginating Stream Not Working with "Join"

I'm paginating through a convex-helpers stream which I'm using to do a "join" and getting strange behavior where the stream ends early.

I'm trying to join both the 
userWants
 and 
userHaves
 table on their 
userId
 and paginate through the results.

Here is my query:

export const matchingTrades = query({
  args: {
    paginationOpts: paginationOptsValidator,
  },
  handler: async (ctx, args) => {
    const me = await getCurrentUser(ctx);

    const myWants = stream(ctx.db, schema)
      .query('userWants')
      .withIndex('by_user', (q) => q.eq('userId', me._id));

    const myTrades = myWants.flatMap(
      async (myWant) => {
        const myHaves = stream(ctx.db, schema)
          .query('userHaves')
          .withIndex('by_user', (q) => q.eq('userId', me._id));

        return myHaves.map(async (myHave) => {
          return {
            userId: me.username,
            want: myWant.cardName,
            have: myHave.cardName,
          };
        });
      },
      ['userId', 'cardId']
    );

    return myTrades.paginate(args.paginationOpts);
  },
});


And here is the relavant part of the schema:
  userWants: defineTable({
    userId: v.id('users'),
    cardId: v.id('cards'),
    cardName: v.optional(v.string()),
    rarityCode: v.string(),
  })
    .index('by_user', ['userId', 'cardId']),

  userHaves: defineTable({
    userId: v.id('users'),
    cardId: v.id('cards'),
    cardName: v.optional(v.string()),
    rarityCode: v.string(),
  })
    .index('by_user', ['userId', 'cardId']),


I'm testing with 3 entries in each table all with the same 
userId
.

If I use 
collect()
 I get the expected count of 3 x 3 = 9.

If I use 
paginate()
 with an 
initialNumItems
 of 9 or more, it works and loads them all.

If 
initialNumItems
 is 1 and I keep calling 
loadMore(1)
 it incorrectly terminates the stream after 3 items.

If 
initialNumItems
 is 4 and I keep calling 
loadMore(1)
 it incorrectly terminates the stream after 6 items.

So something with the cursor gets confused at multiples of the flatMap size.
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