# D1 Database

> Cloudflare D1

- Skill: `comeonoliver/d1-database` (Agent Skill)
- Install (CLI): `npx skillmds@latest add comeonoliver/d1-database`
- Raw SKILL.md: https://api.skillmd.com/api/skills/comeonoliver/d1-database/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: ComeOnOliver (https://skillmd.com/u/comeonoliver)
- Updated: 2026-09-21
- Page: https://skillmd.com/skills/comeonoliver/d1-database

---

# Cloudflare D1

## Overview

D1 is Cloudflare's serverless SQLite database — runs at the edge alongside Workers. Zero connection overhead (it's in the same data center as your Worker), SQLite query syntax, automatic replication, and pay-per-query pricing. Perfect for read-heavy workloads, content sites, and applications where latency matters.

## When to Use

- Building on Cloudflare Workers and need a database
- Read-heavy applications (blogs, content sites, APIs)
- Want SQLite simplicity with global distribution
- Serverless applications with no connection pooling headaches
- Edge-first applications where database latency matters

## Instructions

### Setup

```bash
# Create a D1 database
npx wrangler d1 create my-database

# Add to wrangler.toml
```

```toml
# wrangler.toml
[[d1_databases]]
binding = "DB"
database_name = "my-database"
database_id = "xxxx-xxxx-xxxx"
```

### Schema and Migrations

```bash
# Create migration
npx wrangler d1 migrations create my-database init
```

```sql
-- migrations/0001_init.sql
CREATE TABLE users (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  email TEXT NOT NULL UNIQUE,
  name TEXT NOT NULL,
  created_at TEXT DEFAULT (datetime('now'))
);

CREATE TABLE posts (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  title TEXT NOT NULL,
  content TEXT NOT NULL,
  author_id INTEGER NOT NULL REFERENCES users(id),
  published BOOLEAN DEFAULT FALSE,
  created_at TEXT DEFAULT (datetime('now'))
);

CREATE INDEX idx_posts_author ON posts(author_id);
CREATE INDEX idx_posts_published ON posts(published);
```

```bash
# Apply migrations
npx wrangler d1 migrations apply my-database
```

### Queries in Workers

```typescript
// src/index.ts — Cloudflare Worker with D1
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const url = new URL(request.url);

    if (url.pathname === "/api/posts" && request.method === "GET") {
      const { results } = await env.DB.prepare(
        `SELECT posts.*, users.name as author_name
         FROM posts
         JOIN users ON posts.author_id = users.id
         WHERE posts.published = TRUE
         ORDER BY posts.created_at DESC
         LIMIT ?`
      ).bind(20).all();

      return Response.json({ posts: results });
    }

    if (url.pathname === "/api/posts" && request.method === "POST") {
      const body = await request.json();
      const result = await env.DB.prepare(
        "INSERT INTO posts (title, content, author_id) VALUES (?, ?, ?) RETURNING *"
      ).bind(body.title, body.content, body.authorId).first();

      return Response.json({ post: result }, { status: 201 });
    }

    return new Response("Not found", { status: 404 });
  },
};
```

### With Drizzle ORM

```typescript
// src/db/schema.ts — Drizzle schema for D1
import { sqliteTable, text, integer } from "drizzle-orm/sqlite-core";

export const users = sqliteTable("users", {
  id: integer("id").primaryKey({ autoIncrement: true }),
  email: text("email").notNull().unique(),
  name: text("name").notNull(),
});

export const posts = sqliteTable("posts", {
  id: integer("id").primaryKey({ autoIncrement: true }),
  title: text("title").notNull(),
  content: text("content").notNull(),
  authorId: integer("author_id").notNull().references(() => users.id),
  published: integer("published", { mode: "boolean" }).default(false),
});
```

```typescript
// src/index.ts — Using Drizzle with D1
import { drizzle } from "drizzle-orm/d1";
import { eq } from "drizzle-orm";
import * as schema from "./db/schema";

export default {
  async fetch(request: Request, env: Env) {
    const db = drizzle(env.DB, { schema });

    const publishedPosts = await db.query.posts.findMany({
      where: eq(schema.posts.published, true),
      with: { author: true },
      orderBy: (posts, { desc }) => [desc(posts.id)],
      limit: 20,
    });

    return Response.json({ posts: publishedPosts });
  },
};
```

## Examples

### Example 1: Build a blog API on the edge

**User prompt:** "Create a blog API with Cloudflare Workers and D1 for posts and comments."

The agent will create D1 schema, migrations, CRUD endpoints in a Worker, and Drizzle ORM integration.

### Example 2: User authentication with D1

**User prompt:** "Store user accounts in D1 with email/password auth."

The agent will create users table, password hashing with Web Crypto API, session management, and auth middleware.

## Guidelines

- **SQLite syntax** — D1 is SQLite under the hood
- **Prepared statements with `.bind()`** — prevent SQL injection
- **`.first()` for single row, `.all()` for multiple** — query methods
- **Migrations via Wrangler** — version-controlled schema changes
- **Read replicas are automatic** — D1 replicates globally
- **Write latency is higher** — writes go to primary; reads are fast everywhere
- **5MB row limit** — not for large blobs
- **Free tier: 5M reads, 100K writes/day** — generous for small apps
- **Drizzle ORM recommended** — type-safe queries with D1 adapter
- **Local development** — `wrangler dev` uses local SQLite