Django Backend Development — Level 3 | Build Production APIs

Trace one request from client to response

Explain how an HTTP request enters Django, passes routing/view logic, may touch data, and becomes an HTTP response.

Identify method, path, headers and body

Read a request and separate its method, URL path, headers, query parameters and body.

Choose an appropriate response and status code

Return a response body and status that accurately represent success, validation failure, missing resources or server failure.

Read Django project structure before editing

Locate manage.py, settings, urls, apps and common entry points before changing code.

Distinguish project configuration from app behavior

Explain which concerns belong at project level and which belong inside a reusable app.

Map an incoming feature to likely files

Given a backend requirement, identify the Django modules likely to change before opening the editor.

Explain Django project versus app responsibilities

Describe the project as configuration/integration scope and apps as cohesive feature/domain modules.

Create an app with a clear responsibility boundary

Define an app around a meaningful domain capability rather than arbitrary file grouping.

Register an app without hidden coupling

Connect an app through settings and URLs while keeping ownership and dependencies clear.

Separate configuration from source code

Keep secrets and environment-specific values outside committed application logic.

Read settings from environment safely

Convert and validate environment values instead of assuming all values are strings with correct content.

Classify safe defaults versus required secrets

Decide which settings may have development defaults and which must fail closed when missing.

Map URL patterns to view responsibilities

Connect route shape, path converters and names to the backend behavior they expose.

Use path parameters intentionally

Extract identifiers from URLs and distinguish path identity from query filtering.

Keep URL design stable and readable

Choose resource-oriented paths and names that remain understandable as an application grows.

Read HttpRequest data from the correct source

Distinguish path parameters, query parameters, headers, body/form data and authenticated user context.

Return the right response type

Choose HttpResponse, JsonResponse, redirects or framework API responses based on the endpoint contract.

Use status codes as part of the contract

Select status codes that communicate created, no-content, bad-request, unauthorized, forbidden and not-found outcomes correctly.

Translate domain concepts into model fields

Choose field types and options that represent real domain meaning instead of merely storing convenient values.

Use constraints to protect invalid states

Apply uniqueness, nullability, choices and database constraints where invalid data should be impossible.

Separate stored facts from derived values

Avoid persisting values that can be reliably computed unless there is a clear consistency/performance reason.

Model one-to-one, one-to-many and many-to-many relationships

Choose Django relationship fields that match domain cardinality and ownership.

Choose on_delete behavior deliberately

Select CASCADE, PROTECT, SET_NULL or other behavior based on domain consequences instead of convenience.

Avoid ambiguous reverse relationship naming

Use related_name and model boundaries that make relationship traversal understandable.

Build lazy QuerySets intentionally

Compose filters, excludes and ordering while understanding when database evaluation occurs.

Choose get, first, exists and count correctly

Use retrieval methods based on cardinality and cost instead of interchangeable habit.

Express query conditions clearly

Use field lookups and Q objects where needed without hiding business rules in unreadable query chains.

Detect N+1 access through relationships

Recognize repeated related-object queries caused by naive iteration.

Use select_related for single-valued joins

Fetch foreign-key and one-to-one related rows efficiently when a SQL join fits the access pattern.

Use prefetch_related for multi-valued relationships

Fetch many-related collections in bounded queries and explain why prefetch differs from select_related.

Choose the right validation layer

Decide whether a rule belongs in field validation, model logic, serializer validation or a service boundary.

Return field-specific validation errors

Expose invalid input with structured errors that tell clients exactly what failed.

Prevent validation duplication and drift

Centralize shared domain rules so forms, APIs and services do not disagree about valid state.

Identify operations that require atomicity

Recognize multi-write workflows that must either fully succeed or fully roll back.

Use transaction.atomic around consistency boundaries

Wrap the smallest meaningful unit of database work in a transaction.

Reason about failures inside a transaction

Explain rollback behavior and avoid side effects that cannot be reversed with the database state.

Use Django password handling safely

Create and authenticate users without storing or comparing raw passwords directly.

Explain sessions and authenticated identity

Describe how login establishes session-backed identity and how Django associates later requests with a user.

Choose a custom user strategy early

Recognize when requirements justify a custom user model and why changing later is expensive.

Read request.user as authenticated context

Use authenticated identity in view logic without trusting client-supplied user identifiers for ownership.

Differentiate unauthenticated and authenticated behavior

Design endpoint responses and redirects according to whether identity is known.

Separate authentication from authorization

Explain why proving who a user is does not automatically mean they may perform an action.

Serialize model data into stable API representations

Expose only intended fields and understand representation versus database storage.

Deserialize and validate incoming API data

Use serializers to convert input into validated Python data before writes.

Separate read-only, write-only and writable fields

Control which values clients may see or supply as part of the API contract.

Choose APIView, generic views or ViewSets intentionally

Select DRF view abstractions based on endpoint complexity and reuse needs.

Keep HTTP orchestration separate from domain work

Use views to coordinate request/response behavior while moving reusable domain logic out of controllers.

Trace serializer, permission and queryset flow

Explain the order in which a typical DRF request is authenticated, authorized, validated and persisted.

Explain CSRF protection in cookie-authenticated flows

Describe why browsers can attach cookies automatically and how CSRF tokens protect state-changing requests.

Distinguish authentication cookies from authorization rules

Explain why possession of a valid session cookie still requires backend permission checks.

Choose trust boundaries for browser and API clients

Decide which origins, cookies and credentials are accepted instead of treating all clients equally.

Use ORM parameterization instead of string-built SQL

Avoid injection risks by expressing database queries through safe ORM or parameterized APIs.

Prevent mass assignment of protected fields

Ensure clients cannot set ownership, role, balance or other server-controlled fields simply by including them in input.

Validate file and external input boundaries

Check type, size, format and allowed content before trusting uploaded or external data.

Test model rules and invariants

Write tests that prove model constraints, defaults and domain methods preserve valid state.

Test service-layer behavior independently

Exercise reusable domain operations with controlled inputs instead of relying only on endpoint tests.

Use database tests only where persistence matters

Separate pure logic tests from database-backed tests to keep feedback focused and efficient.

Test successful API behavior

Verify status codes, response shape and persisted side effects for valid authenticated requests.

Test unauthenticated and forbidden cases

Prove endpoints reject missing identity and insufficient permissions correctly.

Test validation and not-found behavior

Cover invalid input, missing resources and boundary cases as first-class backend contracts.

Measure query count before optimizing

Use query evidence to identify expensive request paths instead of guessing from code appearance.

Repair N+1 query patterns

Use relationship loading strategies and query redesign to bound database work.

Verify optimization preserves response behavior

Compare output and tests before and after query changes so speed improvements do not change the contract.

Identify data worth caching

Choose expensive, repeated and sufficiently stable results rather than caching every response.

Define cache key and invalidation rules

Explain what makes cached data unique and when it must expire or be removed.

Detect stale-cache failure modes

Recognize when cache and database disagree and design safe fallback or invalidation behavior.

Load deployment configuration from the environment

Keep production secrets, hosts, database settings and feature flags outside source-controlled defaults.

Run Django deployment checks before release

Use framework checks and a production checklist to catch unsafe settings before traffic arrives.

Separate build-time and runtime configuration

Know which settings belong in the built artifact versus the deployed environment.

Log structured request and error context

Capture useful identifiers, endpoint context and exception evidence without leaking secrets.

Design meaningful health checks

Expose readiness/liveness signals that verify critical dependencies without performing expensive work.

Investigate production failures from evidence

Correlate logs, status codes, request identifiers and recent changes before editing code.

Turn product requirements into API resources

Define actors, use cases, resources, relationships and acceptance criteria before implementation.

Design the data model around invariants

Choose models, constraints and relationships that make invalid domain state difficult to represent.

Plan endpoint contracts before coding

Specify methods, paths, input, output, permissions and failure cases for the final API.

Implement authenticated resource ownership

Create endpoints whose writes bind ownership to the authenticated user and enforce object-level access.

Protect backend behavior with tests

Write success, validation, unauthorized, forbidden and regression tests for critical workflows.

Inspect and improve query performance

Measure request query behavior and remove avoidable repeated database work before final review.