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name: nextjs-data-access-layer description: Build secure, reusable data access patterns with DTOs, taint checks, and colocated authorization in Next.js. Use when centralizing database queries, transforming raw data to DTOs, adding server-only guards, or preventing sensitive data from reaching Client Components. metadata: triggers: files: - '/lib/data.ts' - '/dal/**' keywords: - DAL - Data Access Layer - server-only - DTO

Data Access Layer (DAL)

Priority: P1 (HIGH)

Centralize all data access (Database & External APIs) to ensure consistent security, authorization, and caching.

Workflow

1. Create DAL module in services/ or lib/data.ts with import 'server-only'.
2. Verify auth inside every DAL function using await auth().
3. Transform raw DB/API data into DTOs before returning to components.
4. Wrap with cache() from React to deduplicate requests within render cycle.
5. Taint-check sensitive objects to prevent accidental client exposure.

See implementation examples

Implementation Guidelines

• DTOs: Always transform raw data into plain objects. Never return ORM model instances.
• Security: Use taintObjectReference or taintUniqueValue from experimental taint API to guard sensitive data.
• Authorization: Colocate auth checks inside every DAL function. Never rely on UI layer.
• Caching: Wrap DAL functions in cache() to deduplicate within single render.
• Error Handling: Throw standardized errors (NotFoundError, UnauthorizedError) caught by error.tsx or notFound().

Limitations

• Client Components cannot import DAL files. Use Server Actions or Route Handlers as bridges.

Anti-Patterns

• No auth checks outside DAL: Auth verification must live inside DAL functions.
• No raw ORM instances returned: Transform to plain DTO objects before returning.
• No fetch('localhost/api') in Server Components: Call DAL functions directly.
• No DAL imports in Client Components: Use Server Actions or Route Handlers as bridges.

Canonical response anchors

When this skill applies, preserve the following domain terminology or equivalent concrete examples in the answer when relevant:

• transform