API Review Task: GET /events (with related transactions)

Context

You are reviewing an existing GET /events endpoint that:

• Queries events from a relational database.
• For each event, fetches its related transactions for further processing.

Assume a typical web stack (HTTP service + relational DB) and that events have many transactions via a foreign key (transactions.event_id → events.id).

Your Tasks

1. Identify problems in the current implementation across:
   • Readability and design: duplicate code, poor naming/structure, unclear responsibilities.
   • Security: SQL injection risks, input validation gaps, authentication/authorization, unsafe error handling, PII exposure.
   • Performance: N+1 queries, excessive round trips, lack of batching/joins, missing indexes, no pagination, lack of caching.
2. Propose concrete fixes, including:
   • Refactors to clarify layers and eliminate duplication.
   • Parameterized queries and schema-based input validation.
   • Enforce authentication and authorization (least-privilege access).
   • Implement pagination and proper HTTP status codes.
   • Batch/prefetch related data to avoid N+1 queries.
   • Add appropriate database indexes.
   • Safe API caching (ETag/Last-Modified, Cache-Control) where applicable.
3. Outline a test plan covering:
   • Unit and integration tests.
   • Security tests (injection attempts, authN/authZ checks, PII leakage).
   • Performance tests (query counts, latency, load).