Cloudflare D1 Database

Status: Production Ready ✅ | Last Verified: 2025-11-25

Table of Contents

1. What Is D1?
2. Quick Start
3. Critical Rules
4. D1 API Methods
5. Top 5 Use Cases
6. Migrations Best Practices
7. Common Patterns
8. SQLite Type Affinity
9. Top 5 Errors Prevented

---

What Is D1?

Cloudflare D1 is serverless SQLite on the edge:

• SQL database without servers
• Global distribution
• Zero cold starts
• Standard SQLite syntax
• Read replication for global performance

---

Quick Start (5 Minutes)

1. Create Database

bunx wrangler d1 create my-database

Save the database_id from output!

2. Configure Binding

Add to wrangler.jsonc:

{
  "name": "my-worker",
  "main": "src/index.ts",
  "compatibility_date": "2025-10-11",
  "d1_databases": [
    {
      "binding": "DB",                    // env.DB
      "database_name": "my-database",
      "database_id": "<UUID>",
      "preview_database_id": "local-db"
    }
  ]
}

3. Create Migration

bunx wrangler d1 migrations create my-database create_users

Edit migrations/0001_create_users.sql:

CREATE TABLE IF NOT EXISTS users (
  user_id INTEGER PRIMARY KEY AUTOINCREMENT,
  email TEXT NOT NULL UNIQUE,
  username TEXT NOT NULL,
  created_at INTEGER NOT NULL
);

CREATE INDEX IF NOT EXISTS idx_users_email ON users(email);

PRAGMA optimize;

4. Apply Migration

# Local
bunx wrangler d1 migrations apply my-database --local

# Production
bunx wrangler d1 migrations apply my-database --remote

5. Query from Worker

import { Hono } from 'hono';

type Bindings = {
  DB: D1Database;
};

const app = new Hono<{ Bindings: Bindings }>();

app.get('/users/:email', async (c) => {
  const { results } = await c.env.DB.prepare(
    'SELECT * FROM users WHERE email = ?'
  )
    .bind(c.req.param('email'))
    .all();

  return c.json(results);
});

export default app;

Load references/setup-guide.md for complete walkthrough.

---

Critical Rules

Always Do ✅

1. Use prepared statements with .bind() (never string concatenation)
2. Create indexes for WHERE/JOIN/ORDER BY columns
3. Use migrations for schema changes (never manual SQL)
4. Batch queries for multiple operations (.batch())
5. Run PRAGMA optimize after schema changes
6. Handle errors explicitly (try/catch)
7. Use INTEGER for timestamps (Date.now())
8. Test locally before deploying migrations
9. Use read replicas for global read performance
10. Validate input before SQL queries

Never Do ❌

1. Never concatenate user input into SQL
2. Never commit database_id to public repos
3. Never skip migrations for schema changes
4. Never use VARCHAR (use TEXT instead)
5. Never skip indexes for filtered columns
6. Never ignore SQLite type affinity rules
7. **Never use SELECT *** without LIMIT
8. Never run migrations without testing locally
9. Never exceed 1MB per row
10. Never use DATETIME (use INTEGER for timestamps)

---

D1 API Methods

prepare() - Execute Queries

// Single result
const { results } = await env.DB.prepare(
  'SELECT * FROM users WHERE email = ?'
)
  .bind(email)
  .all();

// First result only
const user = await env.DB.prepare(
  'SELECT * FROM users WHERE user_id = ?'
)
  .bind(userId)
  .first();

// Raw results (faster)
const { results } = await env.DB.prepare(
  'SELECT username FROM users'
)
  .raw();  // Returns arrays instead of objects

batch() - Multiple Queries

const results = await env.DB.batch([
  env.DB.prepare('INSERT INTO users (email, username, created_at) VALUES (?, ?, ?)')
    .bind('user1@example.com', 'user1', Date.now()),
  env.DB.prepare('INSERT INTO users (email, username, created_at) VALUES (?, ?, ?)')
    .bind('user2@example.com', 'user2', Date.now()),
  env.DB.prepare('SELECT COUNT(*) as count FROM users')
]);

console.log('Users count:', results[2].results[0].count);

All queries execute in single transaction (all succeed or all fail).

exec() - Run SQL String

// For migrations/setup only
await env.DB.exec(`
  CREATE TABLE IF NOT EXISTS users (
    user_id INTEGER PRIMARY KEY,
    email TEXT NOT NULL
  );
  CREATE INDEX idx_email ON users(email);
`);

NEVER use for queries with user input!

Load references/query-patterns.md for complete API reference.

---

Top 5 Use Cases

Use Case 1: User CRUD

// Create
app.post('/users', async (c) => {
  const { email, username } = await c.req.json();

  const { results } = await c.env.DB.prepare(
    'INSERT INTO users (email, username, created_at) VALUES (?, ?, ?) RETURNING *'
  )
    .bind(email, username, Date.now())
    .all();

  return c.json(results[0]);
});

// Read
app.get('/users/:id', async (c) => {
  const user = await c.env.DB.prepare(
    'SELECT * FROM users WHERE user_id = ?'
  )
    .bind(c.req.param('id'))
    .first();

  if (!user) {
    return c.json({ error: 'Not found' }, 404);
  }

  return c.json(user);
});

// Update
app.patch('/users/:id', async (c) => {
  const { username } = await c.req.json();

  await c.env.DB.prepare(
    'UPDATE users SET username = ?, updated_at = ? WHERE user_id = ?'
  )
    .bind(username, Date.now(), c.req.param('id'))
    .run();

  return c.json({ success: true });
});

// Delete
app.delete('/users/:id', async (c) => {
  await c.env.DB.prepare(
    'DELETE FROM users WHERE user_id = ?'
  )
    .bind(c.req.param('id'))
    .run();

  return c.json({ success: true });
});

Use Case 2: Batch Operations

app.post('/users/bulk', async (c) => {
  const users = await c.req.json();  // Array of users

  const statements = users.map(user =>
    c.env.DB.prepare(
      'INSERT INTO users (email, username, created_at) VALUES (?, ?, ?)'
    ).bind(user.email, user.username, Date.now())
  );

  const results = await c.env.DB.batch(statements);

  return c.json({ inserted: results.length });
});

Use Case 3: Read Replication (Global Reads)

// Configure read replica (any region)
const session = c.env.DB.withSession({
  preferredRegion: 'auto'  // or 'weur', 'wnam', 'enam', 'apac'
});

// Read from nearest replica
const { results } = await session.prepare(
  'SELECT * FROM users WHERE email = ?'
)
  .bind(email)
  .all();

// Check which region served request
console.log('Served by:', results[0].served_by_region);

Load references/read-replication.md for complete guide.

Use Case 4: Transactions with Batch

// Transfer credits between users (atomic)
const results = await c.env.DB.batch([
  c.env.DB.prepare(
    'UPDATE users SET credits = credits - ? WHERE user_id = ?'
  ).bind(amount, fromUserId),
  c.env.DB.prepare(
    'UPDATE users SET credits = credits + ? WHERE user_id = ?'
  ).bind(amount, toUserId),
  c.env.DB.prepare(
    'INSERT INTO transactions (from_user, to_user, amount, created_at) VALUES (?, ?, ?, ?)'
  ).bind(fromUserId, toUserId, amount, Date.now())
]);

// All succeed or all fail (transaction)

Use Case 5: Pagination

app.get('/users', async (c) => {
  const page = parseInt(c.req.query('page') || '1');
  const limit = 20;
  const offset = (page - 1) * limit;

  const { results } = await c.env.DB.prepare(
    'SELECT * FROM users ORDER BY created_at DESC LIMIT ? OFFSET ?'
  )
    .bind(limit, offset)
    .all();

  return c.json({
    users: results,
    page,
    limit
  });
});

---

Migrations Best Practices

1. Always Use Migrations

bunx wrangler d1 migrations create my-database add_users_avatar

2. Make Migrations Idempotent

-- ✅ GOOD: Idempotent
CREATE TABLE IF NOT EXISTS users (...);
CREATE INDEX IF NOT EXISTS idx_email ON users(email);
DROP TABLE IF EXISTS old_table;

-- ❌ BAD: Fails on re-run
CREATE TABLE users (...);
CREATE INDEX idx_email ON users(email);

3. Test Locally First

bunx wrangler d1 migrations apply my-database --local
bunx wrangler d1 execute my-database --local --command "SELECT * FROM users"

4. Add PRAGMA optimize

-- End of migration
PRAGMA optimize;

Load templates/schema-example.sql for complete schema template.

---

When to Load References

Load references/setup-guide.md when:

• First-time D1 setup
• Creating first database
• Configuring bindings
• Applying first migration

Load references/query-patterns.md when:

• Need complete API reference
• Complex query patterns
• Batch operations
• Error handling

Load references/read-replication.md when:

• Setting up global reads
• Need low latency worldwide
• Understanding Sessions API
• Sequential consistency required

Load references/best-practices.md when:

• Optimizing query performance
• Schema design decisions
• Index strategies
• Production deployment checklist

---

Using Bundled Resources

References (references/)

• setup-guide.md - Complete setup walkthrough
• query-patterns.md - Complete API reference with examples
• read-replication.md - Global read replicas setup
• best-practices.md - Performance and optimization

Templates (templates/)

• schema-example.sql - Complete schema with indexes
• d1-worker-queries.ts - All query patterns in Workers
• d1-setup-migration.sh - Complete setup script

---

Common Patterns

Error Handling

try {
  const { results } = await env.DB.prepare(
    'SELECT * FROM users WHERE email = ?'
  )
    .bind(email)
    .all();

  return c.json(results);
} catch (error) {
  console.error('D1 Error:', error);
  return c.json({ error: 'Database error' }, 500);
}

Raw Mode (Performance)

// Returns arrays instead of objects (faster)
const { results } = await env.DB.prepare(
  'SELECT user_id, email FROM users'
)
  .raw();

// results = [[1, 'user1@example.com'], [2, 'user2@example.com']]

COUNT Queries

const count = await env.DB.prepare(
  'SELECT COUNT(*) as count FROM users'
)
  .first('count');  // Get single column value

console.log('Total users:', count);

---

SQLite Type Affinity

D1 uses SQLite type affinity:

Declared Type	Affinity
INTEGER, INT	INTEGER
TEXT, VARCHAR, CHAR	TEXT
REAL, FLOAT, DOUBLE	REAL
BLOB	BLOB
(no type)	BLOB

Best practices:

• Use INTEGER for numbers
• Use TEXT for strings (not VARCHAR)
• Use INTEGER for timestamps (Date.now())
• Use BLOB for binary data

---

Top 5 Errors Prevented

1. SQL Injection: Use .bind(), never string concatenation
2. Missing Indexes: Create indexes for WHERE/JOIN columns
3. Migration Failures: Test locally first
4. Type Confusion: Use INTEGER for timestamps
5. Batch Size: Limit batch to <500 statements

Load references/best-practices.md for complete error prevention.

---

Official Documentation

• D1 Overview: https://developers.cloudflare.com/d1/
• Get Started: https://developers.cloudflare.com/d1/get-started/
• Client API: https://developers.cloudflare.com/d1/build-with-d1/d1-client-api/
• Read Replication: https://developers.cloudflare.com/d1/reference/read-replication/

---

Questions? Issues?

1. Check references/setup-guide.md for setup
2. Review references/query-patterns.md for API reference
3. See references/read-replication.md for global reads
4. Load references/best-practices.md for optimization