Cloudflare D1 Database

Status: Production Ready ✅ Last Updated: 2025-10-21 Dependencies: cloudflare-worker-base (for Worker setup) Latest Versions: wrangler@4.43.0, @cloudflare/workers-types@4.20251014.0

---

Quick Start (5 Minutes)

1. Create D1 Database

# Create a new D1 database
npx wrangler d1 create my-database

# Output includes database_id - save this!
# ✅ Successfully created DB 'my-database'
#
# [[d1_databases]]
# binding = "DB"
# database_name = "my-database"
# database_id = "<UUID>"

2. Configure Bindings

Add to your wrangler.jsonc:

{
  "name": "my-worker",
  "main": "src/index.ts",
  "compatibility_date": "2025-10-11",
  "d1_databases": [
    {
      "binding": "DB",                    // Available as env.DB in your Worker
      "database_name": "my-database",      // Name from wrangler d1 create
      "database_id": "<UUID>",             // ID from wrangler d1 create
      "preview_database_id": "local-db"    // For local development
    }
  ]
}

CRITICAL:

• binding is how you access the database in code (env.DB)
• database_id is the production database UUID
• preview_database_id is for local dev (can be any string)
• Never commit real database_id values to public repos - use environment variables or secrets

3. Create Your First Migration

# Create migration file
npx wrangler d1 migrations create my-database create_users_table

# This creates: migrations/0001_create_users_table.sql

Edit the migration file:

-- migrations/0001_create_users_table.sql
DROP TABLE IF EXISTS users;
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,
  updated_at INTEGER
);

-- Create index for common queries
CREATE INDEX IF NOT EXISTS idx_users_email ON users(email);

-- Optimize database
PRAGMA optimize;

4. Apply Migration

# Apply locally first (for testing)
npx wrangler d1 migrations apply my-database --local

# Apply to production when ready
npx wrangler d1 migrations apply my-database --remote

5. Query from Your Worker

// src/index.ts
import { Hono } from 'hono';

type Bindings = {
  DB: D1Database;
};

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

app.get('/api/users/:email', async (c) => {
  const email = c.req.param('email');

  try {
    // ALWAYS use prepared statements with bind()
    const result = await c.env.DB.prepare(
      'SELECT * FROM users WHERE email = ?'
    )
    .bind(email)
    .first();

    if (!result) {
      return c.json({ error: 'User not found' }, 404);
    }

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

export default app;

---

D1 Migrations System

Migration Workflow

# 1. Create migration
npx wrangler d1 migrations create <DATABASE_NAME> <MIGRATION_NAME>

# 2. List unapplied migrations
npx wrangler d1 migrations list <DATABASE_NAME> --local
npx wrangler d1 migrations list <DATABASE_NAME> --remote

# 3. Apply migrations
npx wrangler d1 migrations apply <DATABASE_NAME> --local   # Test locally
npx wrangler d1 migrations apply <DATABASE_NAME> --remote  # Deploy to production

Migration File Naming

Migrations are automatically versioned:

migrations/
├── 0000_initial_schema.sql
├── 0001_add_users_table.sql
├── 0002_add_posts_table.sql
└── 0003_add_indexes.sql

Rules:

• Files are executed in sequential order
• Each migration runs once (tracked in d1_migrations table)
• Failed migrations roll back (transactional)
• Can't modify or delete applied migrations

Custom Migration Configuration

{
  "d1_databases": [
    {
      "binding": "DB",
      "database_name": "my-database",
      "database_id": "<UUID>",
      "migrations_dir": "db/migrations",        // Custom directory (default: migrations/)
      "migrations_table": "schema_migrations"   // Custom tracking table (default: d1_migrations)
    }
  ]
}

Migration Best Practices

✅ Always Do:

-- Use IF NOT EXISTS to make migrations idempotent
CREATE TABLE IF NOT EXISTS users (...);
CREATE INDEX IF NOT EXISTS idx_users_email ON users(email);

-- Run PRAGMA optimize after schema changes
PRAGMA optimize;

-- Use transactions for data migrations
BEGIN TRANSACTION;
UPDATE users SET updated_at = unixepoch() WHERE updated_at IS NULL;
COMMIT;

❌ Never Do:

-- DON'T include BEGIN TRANSACTION at start (D1 handles this)
BEGIN TRANSACTION;  -- ❌ Remove this

-- DON'T use MySQL/PostgreSQL syntax
ALTER TABLE users MODIFY COLUMN email VARCHAR(255);  -- ❌ Not SQLite

-- DON'T create tables without IF NOT EXISTS
CREATE TABLE users (...);  -- ❌ Fails if table exists

Handling Foreign Keys in Migrations

-- Temporarily disable foreign key checks during schema changes
PRAGMA defer_foreign_keys = true;

-- Make schema changes that would violate foreign keys
ALTER TABLE posts DROP COLUMN author_id;
ALTER TABLE posts ADD COLUMN user_id INTEGER REFERENCES users(user_id);

-- Foreign keys re-enabled automatically at end of migration

---

D1 Workers API

Type Definitions

// Add to env.d.ts or worker-configuration.d.ts
interface Env {
  DB: D1Database;
  // ... other bindings
}

// For Hono
type Bindings = {
  DB: D1Database;
};

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

prepare() - Prepared Statements (PRIMARY METHOD)

Always use prepared statements for queries with user input.

// Basic prepared statement
const stmt = env.DB.prepare('SELECT * FROM users WHERE user_id = ?');
const bound = stmt.bind(userId);
const result = await bound.first();

// Chained (most common pattern)
const user = await env.DB.prepare('SELECT * FROM users WHERE email = ?')
  .bind(email)
  .first();

Why use prepare():

• ✅ Prevents SQL injection
• ✅ Can be reused with different parameters
• ✅ Better performance (query plan caching)
• ✅ Type-safe with TypeScript

Query Result Methods

.all() - Get All Rows

const { results, meta } = await env.DB.prepare(
  'SELECT * FROM users WHERE created_at > ?'
)
.bind(timestamp)
.all();

console.log(results);  // Array of rows
console.log(meta);     // { duration, rows_read, rows_written }

.first() - Get First Row

// Returns first row or null
const user = await env.DB.prepare('SELECT * FROM users WHERE email = ?')
  .bind('user@example.com')
  .first();

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

.first(column) - Get Single Column Value

// Returns the value of a specific column from first row
const count = await env.DB.prepare('SELECT COUNT(*) as total FROM users')
  .first('total');

console.log(count);  // 42 (just the number, not an object)

.run() - Execute Without Results

// For INSERT, UPDATE, DELETE
const { success, meta } = await env.DB.prepare(
  'INSERT INTO users (email, username, created_at) VALUES (?, ?, ?)'
)
.bind(email, username, Date.now())
.run();

console.log(meta);  // { duration, rows_read, rows_written, last_row_id }

batch() - Execute Multiple Queries

CRITICAL FOR PERFORMANCE: Use batch() to reduce latency.

// Prepare multiple statements
const stmt1 = env.DB.prepare('SELECT * FROM users WHERE user_id = ?').bind(1);
const stmt2 = env.DB.prepare('SELECT * FROM users WHERE user_id = ?').bind(2);
const stmt3 = env.DB.prepare('SELECT * FROM posts WHERE user_id = ?').bind(1);

// Execute all in one round trip
const results = await env.DB.batch([stmt1, stmt2, stmt3]);

console.log(results[0].results);  // Users query 1
console.log(results[1].results);  // Users query 2
console.log(results[2].results);  // Posts query

Batch Behavior:

• Executes sequentially (in order)
• Each statement commits individually (auto-commit mode)
• If one fails, remaining statements don't execute
• Much faster than individual queries (single network round trip)

Batch Use Cases:

// ✅ Insert multiple rows efficiently
const inserts = users.map(user =>
  env.DB.prepare('INSERT INTO users (email, username) VALUES (?, ?)')
    .bind(user.email, user.username)
);
await env.DB.batch(inserts);

// ✅ Fetch related data in parallel
const [user, posts, comments] = await env.DB.batch([
  env.DB.prepare('SELECT * FROM users WHERE user_id = ?').bind(userId),
  env.DB.prepare('SELECT * FROM posts WHERE user_id = ?').bind(userId),
  env.DB.prepare('SELECT * FROM comments WHERE user_id = ?').bind(userId)
]);

exec() - Execute Raw SQL (AVOID IN PRODUCTION)

// Only for migrations, maintenance, and one-off tasks
const result = await env.DB.exec(`
  SELECT * FROM users;
  SELECT * FROM posts;
`);

console.log(result);  // { count: 2, duration: 5 }

NEVER use exec() for:

• ❌ Queries with user input (SQL injection risk)
• ❌ Production queries (poor performance)
• ❌ Queries that need results (exec doesn't return data)

ONLY use exec() for:

• ✅ Running migration SQL files locally
• ✅ One-off maintenance tasks
• ✅ Database initialization scripts

---

Query Patterns

Basic CRUD Operations

Create (INSERT)

// Single insert
const { meta } = await env.DB.prepare(
  'INSERT INTO users (email, username, created_at) VALUES (?, ?, ?)'
)
.bind(email, username, Date.now())
.run();

const newUserId = meta.last_row_id;

// Bulk insert with batch()
const users = [
  { email: 'user1@example.com', username: 'user1' },
  { email: 'user2@example.com', username: 'user2' }
];

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

await env.DB.batch(inserts);

Read (SELECT)

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

// Multiple rows
const { results } = await env.DB.prepare(
  'SELECT * FROM users WHERE created_at > ? ORDER BY created_at DESC LIMIT ?'
)
.bind(timestamp, 10)
.all();

// Count
const count = await env.DB.prepare('SELECT COUNT(*) as total FROM users')
  .first('total');

// Exists check
const exists = await env.DB.prepare('SELECT 1 FROM users WHERE email = ? LIMIT 1')
  .bind(email)
  .first();

if (exists) {
  // Email already registered
}

Update (UPDATE)

const { meta } = await env.DB.prepare(
  'UPDATE users SET username = ?, updated_at = ? WHERE user_id = ?'
)
.bind(newUsername, Date.now(), userId)
.run();

const rowsAffected = meta.rows_written;

if (rowsAffected === 0) {
  // User not found
}

Delete (DELETE)

const { meta } = await env.DB.prepare('DELETE FROM users WHERE user_id = ?')
  .bind(userId)
  .run();

const rowsDeleted = meta.rows_written;

Advanced Queries

Pagination

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

  const [countResult, usersResult] = await c.env.DB.batch([
    c.env.DB.prepare('SELECT COUNT(*) as total FROM users'),
    c.env.DB.prepare('SELECT * FROM users ORDER BY created_at DESC LIMIT ? OFFSET ?')
      .bind(limit, offset)
  ]);

  const total = countResult.results[0].total as number;
  const users = usersResult.results;

  return c.json({
    users,
    pagination: {
      page,
      limit,
      total,
      pages: Math.ceil(total / limit)
    }
  });
});

Joins

const { results } = await env.DB.prepare(`
  SELECT
    posts.*,
    users.username as author_name,
    users.email as author_email
  FROM posts
  INNER JOIN users ON posts.user_id = users.user_id
  WHERE posts.published = ?
  ORDER BY posts.created_at DESC
  LIMIT ?
`)
.bind(1, 10)
.all();

Transactions (Batch Pattern)

D1 doesn't support multi-statement transactions, but batch() provides sequential execution:

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

Note: If any statement fails, the batch stops. This provides some transaction-like behavior.

---

Error Handling

Error Types

try {
  const result = await env.DB.prepare('SELECT * FROM users WHERE user_id = ?')
    .bind(userId)
    .first();
} catch (error: any) {
  // D1 errors have a message property
  const errorMessage = error.message;

  if (errorMessage.includes('D1_ERROR')) {
    // D1-specific error
  } else if (errorMessage.includes('D1_EXEC_ERROR')) {
    // SQL syntax error
  } else if (errorMessage.includes('D1_TYPE_ERROR')) {
    // Type mismatch (e.g., undefined instead of null)
  } else if (errorMessage.includes('D1_COLUMN_NOTFOUND')) {
    // Column doesn't exist
  }

  console.error('Database error:', errorMessage);
  return c.json({ error: 'Database operation failed' }, 500);
}

Common Errors and Fixes

"Statement too long"

// ❌ DON'T: Single massive INSERT
await env.DB.exec(`
  INSERT INTO users (email) VALUES
    ('user1@example.com'),
    ('user2@example.com'),
    ... // 1000 more rows
`);

// ✅ DO: Break into batches
const batchSize = 100;
for (let i = 0; i < users.length; i += batchSize) {
  const batch = users.slice(i, i + batchSize);
  const inserts = batch.map(u =>
    env.DB.prepare('INSERT INTO users (email) VALUES (?)').bind(u.email)
  );
  await env.DB.batch(inserts);
}

"Too many requests queued"

// ❌ DON'T: Fire off many individual queries
for (const user of users) {
  await env.DB.prepare('INSERT INTO users (email) VALUES (?)').bind(user.email).run();
}

// ✅ DO: Use batch()
const inserts = users.map(u =>
  env.DB.prepare('INSERT INTO users (email) VALUES (?)').bind(u.email)
);
await env.DB.batch(inserts);

"D1_TYPE_ERROR" (undefined vs null)

// ❌ DON'T: Use undefined
await env.DB.prepare('INSERT INTO users (email, bio) VALUES (?, ?)')
  .bind(email, undefined);  // ❌ D1 doesn't support undefined

// ✅ DO: Use null for optional values
await env.DB.prepare('INSERT INTO users (email, bio) VALUES (?, ?)')
  .bind(email, bio || null);

Retry Logic

async function queryWithRetry<T>(
  queryFn: () => Promise<T>,
  maxRetries = 3
): Promise<T> {
  for (let attempt = 0; attempt < maxRetries; attempt++) {
    try {
      return await queryFn();
    } catch (error: any) {
      const message = error.message;

      // Retry on transient errors
      const isRetryable =
        message.includes('Network connection lost') ||
        message.includes('storage caused object to be reset') ||
        message.includes('reset because its code was updated');

      if (!isRetryable || attempt === maxRetries - 1) {
        throw error;
      }

      // Exponential backoff
      const delay = Math.min(1000 * Math.pow(2, attempt), 5000);
      await new Promise(resolve => setTimeout(resolve, delay));
    }
  }

  throw new Error('Retry logic failed');
}

// Usage
const user = await queryWithRetry(() =>
  env.DB.prepare('SELECT * FROM users WHERE user_id = ?')
    .bind(userId)
    .first()
);

---

Performance Optimization

Indexes

Indexes dramatically improve query performance for filtered columns.

When to Create Indexes

// ✅ Index columns used in WHERE clauses
CREATE INDEX idx_users_email ON users(email);

// ✅ Index foreign keys
CREATE INDEX idx_posts_user_id ON posts(user_id);

// ✅ Index columns used for sorting
CREATE INDEX idx_posts_created_at ON posts(created_at DESC);

// ✅ Multi-column indexes for complex queries
CREATE INDEX idx_posts_user_published ON posts(user_id, published);

Test Index Usage

-- Check if index is being used
EXPLAIN QUERY PLAN SELECT * FROM users WHERE email = 'user@example.com';

-- Should see: SEARCH users USING INDEX idx_users_email

Partial Indexes

-- Index only non-deleted records
CREATE INDEX idx_users_active ON users(email) WHERE deleted = 0;

-- Index only published posts
CREATE INDEX idx_posts_published ON posts(created_at DESC) WHERE published = 1;

PRAGMA optimize

Run after creating indexes or making schema changes:

-- In your migration file
CREATE INDEX idx_users_email ON users(email);
PRAGMA optimize;

Or from Worker:

await env.DB.exec('PRAGMA optimize');

Query Optimization Tips

// ✅ Use specific columns instead of SELECT *
const users = await env.DB.prepare(
  'SELECT user_id, email, username FROM users'
).all();

// ✅ Use LIMIT to prevent scanning entire table
const latest = await env.DB.prepare(
  'SELECT * FROM posts ORDER BY created_at DESC LIMIT 10'
).all();

// ✅ Use indexes for WHERE conditions
// Create index first: CREATE INDEX idx_users_email ON users(email)
const user = await env.DB.prepare('SELECT * FROM users WHERE email = ?')
  .bind(email)
  .first();

// ❌ Avoid functions in WHERE (can't use indexes)
// Bad: WHERE LOWER(email) = 'user@example.com'
// Good: WHERE email = 'user@example.com' (store email lowercase)

---

Local Development

Local vs Remote Databases

# Create local database (automatic on first --local command)
npx wrangler d1 migrations apply my-database --local

# Query local database
npx wrangler d1 execute my-database --local --command "SELECT * FROM users"

# Query remote database
npx wrangler d1 execute my-database --remote --command "SELECT * FROM users"

Local Database Location

Local D1 databases are stored in:

.wrangler/state/v3/d1/miniflare-D1DatabaseObject/<database_id>.sqlite

Seeding Local Database

# Create seed file
cat > seed.sql << 'EOF'
INSERT INTO users (email, username, created_at) VALUES
  ('alice@example.com', 'alice', 1698000000),
  ('bob@example.com', 'bob', 1698000060);
EOF

# Apply seed
npx wrangler d1 execute my-database --local --file=seed.sql

---

Drizzle ORM (Optional)

While D1 works great with raw SQL, some developers prefer ORMs. Drizzle ORM supports D1:

npm install drizzle-orm
npm install -D drizzle-kit

Note: Drizzle adds complexity and another layer to learn. For most D1 use cases, raw SQL with wrangler is simpler and more direct. Only consider Drizzle if you:

• Prefer TypeScript schema definitions over SQL
• Want auto-complete for queries
• Are building a very large application with complex schemas

Official Drizzle D1 docs: https://orm.drizzle.team/docs/get-started-sqlite#cloudflare-d1

---

Best Practices Summary

✅ Always Do:

1. Use prepared statements with .bind() for user input
2. Use .batch() for multiple queries (reduces latency)
3. Create indexes on frequently queried columns
4. Run PRAGMA optimize after schema changes
5. Use IF NOT EXISTS in migrations for idempotency
6. Test migrations locally before applying to production
7. Handle errors gracefully with try/catch
8. Use null instead of undefined for optional values
9. Validate input before binding to queries
10. Check meta.rows_written after UPDATE/DELETE

❌ Never Do:

1. Never use .exec() with user input (SQL injection risk)
2. Never hardcode database_id in public repos
3. Never use undefined in bind parameters (causes D1_TYPE_ERROR)
4. Never fire individual queries in loops (use batch instead)
5. Never forget LIMIT on potentially large result sets
6. Never use SELECT * in production (specify columns)
7. Never include BEGIN TRANSACTION in migration files
8. Never modify applied migrations (create new ones)
9. Never skip error handling on database operations
10. Never assume queries succeed (always check results)

---

Known Issues Prevented

Issue	Description	How to Avoid
Statement too long	Large INSERT statements exceed D1 limits	Break into batches of 100-250 rows
Transaction conflicts	BEGIN TRANSACTION in migration files	Remove BEGIN/COMMIT (D1 handles this)
Foreign key violations	Schema changes break foreign key constraints	Use PRAGMA defer_foreign_keys = true
Rate limiting / queue overload	Too many individual queries	Use batch() instead of loops
Memory limit exceeded	Query loads too much data into memory	Add LIMIT, paginate results, shard queries
Type mismatch errors	Using undefined instead of null	Always use null for optional values

---

Wrangler Commands Reference

# Database management
wrangler d1 create <DATABASE_NAME>
wrangler d1 list
wrangler d1 delete <DATABASE_NAME>
wrangler d1 info <DATABASE_NAME>

# Migrations
wrangler d1 migrations create <DATABASE_NAME> <MIGRATION_NAME>
wrangler d1 migrations list <DATABASE_NAME> --local|--remote
wrangler d1 migrations apply <DATABASE_NAME> --local|--remote

# Execute queries
wrangler d1 execute <DATABASE_NAME> --local|--remote --command "SELECT * FROM users"
wrangler d1 execute <DATABASE_NAME> --local|--remote --file=./query.sql

# Time Travel (view historical data)
wrangler d1 time-travel info <DATABASE_NAME> --timestamp "2025-10-20"
wrangler d1 time-travel restore <DATABASE_NAME> --timestamp "2025-10-20"

---

Official Documentation

• D1 Overview: https://developers.cloudflare.com/d1/
• Get Started: https://developers.cloudflare.com/d1/get-started/
• Migrations: https://developers.cloudflare.com/d1/reference/migrations/
• Workers API: https://developers.cloudflare.com/d1/worker-api/
• Best Practices: https://developers.cloudflare.com/d1/best-practices/
• Wrangler Commands: https://developers.cloudflare.com/workers/wrangler/commands/#d1

---

Ready to build with D1! 🚀