Issue with filtering out nulls from a promise.all mapping over some document ids

[barren lava]

export const getById = zQuery({
  args: { id: zid('videoCollection') },
  handler: async (ctx, { id }) => {
    // Get the collection
    const collection = await ctx.db.get(id)
    if (!collection) return null

    // Get the videos from the collection videos
    const videos = await Promise.all(collection.videos.map((videoId) => ctx.db.get(videoId))).then(
      (results) => results.filter((r) => r !== null),
    ) // <- ISSUE: this currently returns null, even with the filter, because ctx.db.get() can return null

    // Enrich the videos
    const enrichedVideos = await Promise.all(videos.map(async (video) => enrichVideo(ctx, video)))

    // Return the collection including the videos
    return { title: collection.title, videos }
  },
})

Tried quite a few different methods of filtering out the nulls from this promise.all. Unsure if this approach is just generally not the way to go about it?

Am i on the wrong track here

Issue with filtering out nulls from a promise.all mapping over some document ids

[barren lava]

Hmm, this type guard seems to do the trick, still open for other potentially better solutions if anyone else has played around with this themselves:

 // Get the videos from the collection videos
  const videos = (
      await Promise.all(collection.videos.map((videoId) => ctx.db.get(videoId)))
    ).filter((video): video is NonNullable<Doc<'video'>> => video !== null)

[urban knot]

Just filter the whole array after mapping. You can also enrich in the initial mapping to pair things down:

export const getById = zQuery({
  args: { id: zid('videoCollection') },
  handler: async (ctx, { id }) => {
export const getById = zQuery({
  args: { id: zid('videoCollection') },
  handler: async (ctx, { id }) => {
    const collection = await ctx.db.get(id)
    if (!collection) return null

    const videos = (await Promise.all(
      collection.videos.map(async (videoId) => {
        const video = await ctx.db.get(videoId)
        if (video) {
          return enrichVideo(ctx, video)
        }
      }),
    )).filter(Boolean)

    return { title: collection.title, videos }
  },
})

  },
})

Wrapping the awaited Promise.all in parens allows us to filter directly on the resulting array. Boolean as a filter just drops everyting that isn't truthy.

[barren lava]

Actually i had tried the .filter(Boolean) at first, but you've just made me realise what was missing. The freaking async and await inside of the map

I had tried that before, storing it in a const and then checking if video, but my lack of making it async, still caused the null, so i moved onto trying a different solution 😆

It all makes sense now - thanks mate

[barren lava]

Ended up adding a type predicate, so only valid videos are getting returned:

function isValidVideo(video: any): video is VideoEnriched {
  return video !== undefined && video !== null
}

[urban knot]

Were you still getting nulls or was it an issue with the enrich function

[barren lava]

Getting undefined was the issue. From what i could tell, the map just returned undefined if video was false

And i wanted to make sure i got back neither undefined videos or null. But only valid videos

Even though the type guard works perfectly fine. Cant help but to think whether I’m just completely misunderstanding something here.