How do CORS settings work in FastAPI?
CORS middleware tells browsers which frontends are allowed to call your API across origins.
- Browser security feature
- Allow only needed origins
- Credentials require extra care
Quick recall
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How do you handle authentication in FastAPI?
Authentication is often implemented through dependencies that validate tokens, sessions, or API keys before route logic runs.
- Security dependencies are reusable
- Keep auth separate from handler body
- Return clear unauthorized responses
How does dependency injection work in FastAPI?
FastAPI resolves declared dependencies for each request and injects their return values into path operations.
- Uses Depends
- Supports nesting
- Great for auth and shared resources
How does FastAPI generate OpenAPI docs?
FastAPI builds OpenAPI schemas from type hints, route definitions, and Pydantic models automatically.
- Docs are generated from code
- Swagger UI comes built in
- Types drive schema shape
Sync vs async endpoints in FastAPI
Choose async for non-blocking I O and sync for blocking libraries or straightforward CPU-bound logic.
- Both are supported
- Wrong async usage can be slower
- Match the endpoint to the dependency stack
What are background tasks in FastAPI?
Background tasks run lightweight follow-up work after sending the HTTP response.
- Good for email or audit logs
- Still runs in same process
- Not a replacement for a job queue
What are response models in FastAPI?
Response models define the shape of outgoing data, helping validation, filtering, and API documentation.
- Controls output contract
- Can hide internal fields
- Improves docs accuracy
What is lifespan in FastAPI?
Lifespan hooks run application startup and shutdown logic such as opening shared clients or closing resources cleanly.
- Startup for shared setup
- Shutdown for cleanup
- Useful for pools and model loading
Why use Pydantic models in FastAPI?
Pydantic models validate request and response data and generate clear API schemas.
- Parsing plus validation
- Type hints drive docs
- Good error messages
Explain ACID
ACID stands for atomicity, consistency, isolation, and durability.
- Atomicity means all or nothing
- Isolation controls concurrency visibility
- Durability survives crashes after commit
Explain SQL joins
Joins combine rows from tables based on a related key, with inner and outer joins deciding what unmatched rows survive.
- INNER keeps matches
- LEFT keeps all left rows
- Join condition matters
HAVING vs WHERE in SQL
WHERE filters rows before grouping, while HAVING filters groups after aggregation.
- WHERE happens earlier
- HAVING works on grouped results
- Common with aggregate conditions