TaskFlow API – Refactored and Optimized (Developer Notes)

🔍 Core Issues Identified

1. Multiple DB Calls in several service methods (findOne, remove, etc.).

2. No caching layer, causing repeated DB hits for identical queries.

3. Unoptimized filtering — previously done in-memory, not at the DB level.

4. Improper error handling and inconsistent repository usage.

5. Inconsistent field naming (due-date vs dueDate) causing DTO mismatches.

6. JWT secret misconfiguration and environment variable inconsistency.

7. Missing transactional control for job queue integration.

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⚙️ Architectural Improvements

• Redis caching integration (for query-heavy endpoints like findAll, getStats).

• QueryBuilder-based pagination & filtering (no in-memory filtering).

• Transactional job enqueueing — queue jobs added after successful commit to avoid stale tasks.

• Optimized repository pattern usage to reduce redundant queries.

• Consistent DTO naming and schema alignment for dueDate.

• JWT strategy cleanup — environment variable renamed to JWT_SECRET.

• Centralized error handling using NestJS NotFoundException and InternalServerErrorException.

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🚀 Performance & Security Enhancements

• Added Redis caching (via @nestjs/cache-manager) to minimize DB load.

• Cache invalidation handled automatically after create/update/delete operations.

• Background job retries with exponential backoff using BullMQ.

• All DB operations wrapped in TypeORM transactions for data integrity.

• JWT secret stored securely via environment variable (JWT_SECRET).

• Removed duplicate DB queries and replaced with optimized QueryBuilder operations.

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🧩 Key Technical Decisions

Decision	Rationale
Redis caching	Reduces DB calls for read-heavy endpoints.
QueryBuilder for filtering	Enables efficient DB-level filtering & pagination.
Transactions + BullMQ	Ensures data consistency before job enqueue.
Consistent DTO schema	Prevents mismatches between code & DB schema.
Centralized logging	Helps trace background job or DB failures.

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⚖️ Trade-offs

• Slight overhead for maintaining cache invalidation logic.

• Redis adds infrastructure complexity but provides significant performance gain.

• Transactions may introduce minimal latency, but ensure data consistency.

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🧱 Files Modified & Summary

File	Description
src/modules/tasks/tasks.service.ts	Major refactor — added Redis cache, optimized DB calls, transactional queue integration.
src/modules/tasks/dto/task-filter.dto.ts	Added pagination & filtering support.
src/modules/tasks/dto/create-task.dto.ts	Fixed naming conflict (dueDate field).
src/modules/tasks/tasks.controller.ts	Updated endpoints to align with new service structure.
src/modules/tasks/task-processor.service.ts	Handles background jobs with retry/backoff.
src/modules/schedule-tasks/schedule-tasks.module.ts	Imported TypeOrmModule & registered Task entity.
src/auth/jwt.strategy.ts	Changed env variable to JWT_SECRET.

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🧭 Developer Notes

• After every new service or module creation, register it in its corresponding controller.

• Maintain consistent DTO validation and naming across all modules.

• Verify Redis caching using redis-cli monitor or by adding console.log for cache hits/misses.