N+1 that silently drops rows Debugging Lab

N+1 that silently drops rowsDatabaseMediumPreparing workspaceAutosaved

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Incident Dossier

N+1 that silently drops rows

The customer-support view that lists 'every user with their most recent order' is missing the orders. Every user appears in the listing but with no order attached, and no error is raised. The per-user fetch helper is being invoked in a loop and silently returning null.

Initial failing signalEvery user shows latestOrder=nullExpected fetchLatestOrderForUser(1) returns order id 1002 · received fetchLatestOrderForUser(1) returns null because the filter matches nothing

Progress

1Reproduce the bugRun checks

2Edit the fixOpen

3Pass checksOpen

4Submit fixOpen

Reproduction Steps

Run npm test.
Notice that fetchLatestOrderForUser returns null for users who clearly have orders in the fixture.
Trace the failure inside the per-row helper — it iterates the orders table but never matches anything.
Identify the column-name mismatch and align the comparator with the actual property name on the order row.

Focus Mode

Start

src/users.js

Likely area

src/users.js

Progressive hints

Hints reveal broad direction first, then narrow toward the suspect path without showing hidden tests or exact solution code.

TopicDatabase

DifficultyMedium

Est. time20 min

Workspacecreating

Explorer

Preparing workspace files…

Evidence Map

Failing signal loaded from challenge API
Workspace files loaded from workspace API
Results rendered only after API run/submit

Autosaved

workspace

Outputread-onlyready$ workspace boot

Workspace booting...