What is Django middleware?
Middleware is a request and response processing layer that runs around the view.
- Runs in order on request
- Runs reverse order on response
- Good for auth, logging, headers
Quick recall
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What is Django queryset laziness?
QuerySets are lazy, so they usually do not hit the database until they are evaluated.
- Filter chaining stays cheap
- Evaluation happens on iteration or list conversion
- Important for performance reasoning
What is Django REST vs regular Django views?
Regular Django views often render HTML, while API-style views return structured data like JSON for clients or frontend apps.
- HTML response vs data response
- Different consumer types
- Validation and serialization become central in APIs
What is Django's messages framework?
The messages framework stores one-time feedback like success, warning, or error notices across a redirect.
- Useful after POST redirects
- Good for user feedback
- Message levels help template styling
What is the difference between get and filter in Django ORM?
`get()` expects exactly one row and raises errors otherwise, while `filter()` returns a QuerySet that can contain zero or more rows.
- get returns one object
- filter returns QuerySet
- Use get only when uniqueness is expected
What is the purpose of Django forms?
Django forms combine HTML rendering, input parsing, validation, and cleaned data handling in one layer.
- Centralizes validation
- Protects against common input errors
- ModelForm reduces CRUD boilerplate
What is the role of Django settings modules?
The settings module controls project-wide configuration such as database connections, installed apps, middleware, and environment-specific behavior.
- Central config layer
- Often split by environment
- Sensitive values should come from env vars
When should you use Django signals?
Signals are useful for decoupled side effects, but too many hidden signal handlers can make code harder to reason about.
- Good for secondary actions
- Bad for core business flow
- Prefer explicit services when logic is important
Why do Django migrations matter?
Migrations version the schema so database changes stay reproducible across environments.
- Model change to schema change
- Stored as code
- Supports rollback and history
async and await in FastAPI
Use async endpoints when the work awaits non-blocking I O; sync endpoints are fine for CPU work or blocking libraries.
- Async improves concurrency for waits
- Do not block the event loop
- Choose library support carefully
Exception handling in FastAPI
Raise HTTPException for expected API errors and register handlers for shared error formatting.
- Use status codes intentionally
- Return structured detail
- Centralize repeated handling
FastAPI middleware basics
Middleware wraps the ASGI request-response cycle for cross-cutting behaviors such as timing, headers, and logging.
- Runs around every request
- Useful for tracing and headers
- Keep it lightweight