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

Status Codes

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