optimize-loader

Optimize Loader

Anti-patterns to catch

1. Re-fetching data the caller already has

If a loader fetches a record (e.g. getVideoWithClipsById) and then passes just the ID to a downstream function that re-fetches the same record internally — change the downstream function's signature to accept the already-fetched object.

// BAD — getNextVideoId internally calls getVideoWithClipsById again
const video = yield * db.getVideoWithClipsById(videoId);
const nextId = yield * db.getNextVideoId(videoId);

// GOOD — pass the already-fetched video
const video = yield * db.getVideoWithClipsById(videoId);
const nextId = yield * db.getNextVideoId(video);

When refactoring signatures, type the parameter as the minimal shape needed, not the full return type:

// Accept only what the function actually reads
function* (currentVideo: {
  id: string;
  lesson: {
    id: string;
    videos: Array<{ id: string; path: string }>;
    section: { repoVersion: { repo: { id: string } } };
  } | null;
})

2. Over-fetching nested relations

If a function only needs IDs and paths for navigation but loads full nested trees including clips, transcripts, etc. — create a slim query variant.

// BAD — loads clips, chapters, thumbnails etc. just to get video IDs
const course = yield * getCourseWithSectionsById(repoId);

// GOOD — dedicated lightweight query
const course = yield * getCourseNavigationData(repoId);

Slim query checklist:

• columns: { id: true, path: true } — only select needed columns on leaf relations
• limit: 1 on relations like versions where you only need the latest
• Omit with: for relations you don't traverse (clips, chapters, thumbnails)
• Keep where: filters (e.g. archived = false) and orderBy intact

3. Sequential independent queries

If a loader runs multiple independent DB calls sequentially, parallelize with Effect.all:

// BAD — sequential, total time = sum of both
const nextVideoId = yield * db.getNextVideoId(video);
const previousVideoId = yield * db.getPreviousVideoId(video);

// GOOD — parallel, total time = max of both
const [nextVideoId, previousVideoId] =
  yield * Effect.all([db.getNextVideoId(video), db.getPreviousVideoId(video)]);

Dependency injection pattern

When adding a new query (like getCourseNavigationData) that lives in course operations but is used by video operations:

1. Add the query to db-course-operations.server.ts and export it
2. Declare the cross-domain dependency in VideoOperationsService's effect block via yield* CourseOperationsService
3. The Effect Layer system resolves cross-domain dependencies automatically