Backend Developer Cheat Sheet

Backend Developer Cheat Sheet

APIs, databases, and server-side development quick reference.

Quick Reference

# Test API endpoint
curl -s http://localhost:8000/api/health | jq .

# Database quick check
psql -c "SELECT count(*) FROM users;"

# Run tests
pytest tests/ -v --tb=short

REST API Design

HTTP Methods

Method	Use Case	Idempotent
GET	Read resource	Yes
POST	Create resource	No
PUT	Replace resource	Yes
PATCH	Update resource	No
DELETE	Remove resource	Yes

Status Codes

Code	Meaning	Use When
200	OK	Success
201	Created	Resource created
204	No Content	Success, no body
400	Bad Request	Invalid input
401	Unauthorized	Auth required
403	Forbidden	No permission
404	Not Found	Resource missing
422	Unprocessable	Validation failed
500	Server Error	Bug/crash

cURL Commands

# GET request
curl -s http://api/users | jq .

# POST with JSON
curl -X POST http://api/users \
  -H "Content-Type: application/json" \
  -d '{"name":"John","email":"[email protected]"}'

# With auth token
curl -H "Authorization: Bearer TOKEN" http://api/users

# PUT request
curl -X PUT http://api/users/1 \
  -H "Content-Type: application/json" \
  -d '{"name":"Updated"}'

# DELETE
curl -X DELETE http://api/users/1

# Verbose output
curl -v http://api/health

# Time request
curl -w "@curl-format.txt" -o /dev/null -s http://api/users

SQL Quick Reference

Common Queries

-- Select with joins
SELECT u.name, o.total
FROM users u
JOIN orders o ON u.id = o.user_id
WHERE o.created_at > NOW() - INTERVAL '7 days';

-- Aggregation
SELECT status, COUNT(*), AVG(total)
FROM orders
GROUP BY status
HAVING COUNT(*) > 10;

-- Subquery
SELECT * FROM users
WHERE id IN (SELECT user_id FROM orders WHERE total > 100);

-- Window function
SELECT name, total,
  RANK() OVER (ORDER BY total DESC) as rank
FROM orders;

Performance

-- Explain query plan
EXPLAIN ANALYZE SELECT * FROM users WHERE email = '[email protected]';

-- Index usage
SELECT indexrelname, idx_scan, idx_tup_read
FROM pg_stat_user_indexes;

-- Table stats
SELECT relname, n_tup_ins, n_tup_upd, n_tup_del
FROM pg_stat_user_tables;

-- Current queries
SELECT pid, query, state, wait_event_type
FROM pg_stat_activity
WHERE state != 'idle';

Redis Commands

# Connection
redis-cli
redis-cli -h host -p 6379 -a password

# Strings
SET key "value"
GET key
SETEX key 3600 "value"  # With TTL

# Lists
LPUSH mylist "item"
LRANGE mylist 0 -1

# Hashes
HSET user:1 name "John"
HGET user:1 name
HGETALL user:1

# Cache pattern
GET cache:users:1 || (fetch from DB, SET cache:users:1)

# Keys
KEYS "pattern:*"
TTL key
DEL key
FLUSHDB  # Clear current DB

Authentication

JWT Structure

Header.Payload.Signature

Header: {"alg":"HS256","typ":"JWT"}
Payload: {"sub":"1234567890","name":"John","iat":1516239022}

Token Verification

import jwt

# Decode
payload = jwt.decode(token, SECRET_KEY, algorithms=["HS256"])

# Create
token = jwt.encode({"sub": user_id, "exp": expiry}, SECRET_KEY)

Testing

# Run tests
pytest tests/ -v
pytest tests/test_users.py -k "test_create"
pytest tests/ --cov=app --cov-report=html

# Mock external services
# Use pytest-mock, responses, or httpretty

Common Patterns

# Pagination
GET /users?page=1&per_page=20

# Filtering
GET /users?status=active&role=admin

# Sorting
GET /users?sort=-created_at

# Rate limiting headers
X-RateLimit-Limit: 100
X-RateLimit-Remaining: 95
X-RateLimit-Reset: 1609459200