Cloudflare D1 Migrations & Production Seeding Skill

Purpose

You are a specialized assistant for schema and data lifecycle of Cloudflare D1 databases, used typically with Hono + TypeScript apps running on Cloudflare Workers/Pages.

Use this skill to:

• Design and evolve D1 schemas using SQL (not ad-hoc changes in the UI)
• Set up and manage D1 migrations via Wrangler
• Implement safe migration workflows for dev, staging, and production
• Create seed scripts/data for development & test
• Help with data migrations (changing schema without losing data)
• Keep D1 usage predictable and reproducible across environments

Do not use this skill for:

• Hono routing or business logic → hono-app-scaffold, feature skills
• D1 query code in TypeScript → hono-d1-integration (that skill handles data access layer)
• Non-D1 databases (Postgres/MySQL/etc.) → use other DB skills

If CLAUDE.md or existing docs describe DB conventions (naming, migrations folder, tenant strategy), follow them.

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When To Apply This Skill

Trigger this skill when the user says things like:

• “Set up migrations for D1.”
• “Create/modify tables in D1 in a structured way.”
• “Apply schema changes across dev/staging/prod.”
• “Seed test data into my D1 database.”
• “Help me evolve this D1 schema safely.”
• “My D1 schema in prod is out of sync, fix the process.”

Avoid when:

• Only a single dev-only prototype DB is used with no need for consistency.
• Schema is fully managed externally and NOT via SQL/migrations in this repo.

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Core Concepts for This Skill

• Schema is code: D1 schema should be defined via SQL files in the repo.
• Migrations are ordered: Each change is a migration with a timestamp/sequence.
• Environments differ: dev/staging/prod may have different DBs, but same migrations.
• Seeds are environment-aware: dev/test seeds can differ from prod initial data.

This skill assumes that:

• D1 is bound in wrangler.toml as DB (or some project-defined name).
• The project has or will have a db/ or migrations/ directory for SQL.

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Recommended Project Structure

project-root/
  src/
    db/
      schema.sql               # initial base schema
  db/
    migrations/
      0001_init.sql
      0002_add_posts_table.sql
      0003_add_indexes.sql
    seeds/
      dev.seed.sql
      test.seed.sql
  wrangler.toml

Note: location is flexible as long as Wrangler commands reference the correct path.

This skill will adapt structure to the existing repo but keep these concepts.

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Defining Initial Schema (schema.sql)

For a new project, start with a base schema file:

-- src/db/schema.sql or db/schema.sql

CREATE TABLE IF NOT EXISTS users (
  id TEXT PRIMARY KEY,
  email TEXT NOT NULL UNIQUE,
  password_hash TEXT NOT NULL,
  created_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
  updated_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now'))
);

CREATE TABLE IF NOT EXISTS posts (
  id TEXT PRIMARY KEY,
  user_id TEXT NOT NULL,
  title TEXT NOT NULL,
  body TEXT NOT NULL,
  created_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
  FOREIGN KEY (user_id) REFERENCES users(id)
);

Use this as the canonical source of truth for the initial DB state.

To apply schema.sql to a local dev DB:

wrangler d1 execute <db_name> --local --file=src/db/schema.sql

This skill will:

• Encourage a clean, normalized initial schema.
• Align SQL with Types (User, Post, etc.) defined in hono-d1-integration skill.

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Migrations: Creating & Applying

Do not re-run schema.sql as a way to “update” prod. Instead, use migrations.

Creating a Migration

Use Wrangler to create a migration file (name is a description):

wrangler d1 migrations create <db_name> add_comments_table

This creates a new SQL file under the migrations folder, e.g.:

db/migrations/
  0001_init.sql
  0002_add_comments_table.sql   # created by wrangler

Edit the new migration file:

-- db/migrations/0002_add_comments_table.sql

CREATE TABLE comments (
  id TEXT PRIMARY KEY,
  post_id TEXT NOT NULL,
  user_id TEXT NOT NULL,
  body TEXT NOT NULL,
  created_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
  FOREIGN KEY (post_id) REFERENCES posts(id),
  FOREIGN KEY (user_id) REFERENCES users(id)
);

This skill should:

• Ensure migrations are append-only (don’t edit old migrations after applying to any environment).
• Encourage small, focused migrations with clear names.

Applying Migrations (Local / Dev)

To apply all pending migrations to local dev DB:

wrangler d1 migrations apply <db_name> --local

This will run all migrations that haven’t been applied yet.

For Cloud/prod DB:

wrangler d1 migrations apply <db_name>

This skill should recommend:

• Apply migrations to staging before production.
• Run migrations as part of a deploy or a separate pre-deploy step (via CI/CD).

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Migration Strategy Across Environments

Assume wrangler.toml contains environment-specific D1 bindings:

[[d1_databases]]
binding = "DB"
database_name = "my_db_dev"
database_id = "dev-xxxx"

[env.staging]
[[env.staging.d1_databases]]
binding = "DB"
database_name = "my_db_staging"
database_id = "staging-xxxx"

[env.production]
[[env.production.d1_databases]]
binding = "DB"
database_name = "my_db_prod"
database_id = "prod-xxxx"

Then, the typical workflow:

• Dev DB (local):
  • wrangler d1 migrations apply my_db_dev --local
• Staging DB:
  • wrangler d1 migrations apply my_db_staging --env staging
• Production DB:
  • wrangler d1 migrations apply my_db_prod --env production

This skill can:

• Provide canonical commands tailored to the project’s actual names.

• Suggest adding scripts in package.json to make this repeatable, e.g.:

  {
    "scripts": {
      "db:migrate:local": "wrangler d1 migrations apply my_db_dev --local",
      "db:migrate:staging": "wrangler d1 migrations apply my_db_staging --env staging",
      "db:migrate:prod": "wrangler d1 migrations apply my_db_prod --env production"
    }
  }
  

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Data Seeding

Seed Files

Use SQL seed files for dev/test:

-- db/seeds/dev.seed.sql
INSERT INTO users (id, email, password_hash)
VALUES
  ("u1", "dev1@example.com", "HASH1"),
  ("u2", "dev2@example.com", "HASH2");

INSERT INTO posts (id, user_id, title, body)
VALUES
  ("p1", "u1", "Hello dev", "First dev post");

Applying Seeds

For local dev:

wrangler d1 execute <db_name> --local --file=db/seeds/dev.seed.sql

For test DBs you might:

• Use a smaller or more targeted seed file (test.seed.sql).
• Or use in-test setup scripts that insert data programmatically (using D1 and Hono test helpers).

This skill will:

• Emphasize that prod environments rarely use “seed files” beyond initial, intentional bootstrapping (like initial admin user). Those should be careful, one-off migrations or controlled operations.

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Schema Evolution / Data Migration

When changing schema in a non-trivial way (e.g., splitting a column, renaming), this skill should:

1. Plan for multi-step migrations:

   Example: rename username to handle

   -- Step 1: add new column
   ALTER TABLE users ADD COLUMN handle TEXT;
   
   -- Step 2: copy data
   UPDATE users SET handle = username;
   
   -- Step 3: (later) drop old column if safe
   

2. Avoid destructive actions that lose data without an explicit backup/migration plan.

3. For large data sets, warn about expensive operations and suggest phased rollouts if needed.

The skill will also:

• Ensure changes in TS types/entities (from hono-d1-integration) match the new schema.
• Suggest adding “backfill” scripts or migrations when needed.

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Coordination With Application Code

This skill must coordinate schema changes with code changes:

• Additive changes (new columns with defaults) are usually safe to deploy before code that uses them.
• Destructive changes (drop columns, change types) require:
  • Rolling deploys where old code can still run for a while.
  • Possibly a “compat layer” or phased roll-out.
• Versioned APIs: For major schema reworks, consider versioned routes (/v1, /v2) temporarily.

The skill should help sequence:

1. Add new columns / tables.
2. Deploy code that writes to both old & new where needed.
3. Backfill data.
4. Switch reads to new columns.
5. Drop old columns.

Even if simplified, it must emphasize not to break prod accidentally.

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Integration with CI/CD

Though CI specifics belong to a separate skill (e.g., cloudflare-ci-cd-github-actions), this skill should:

• Suggest running wrangler d1 migrations apply against staging/prod as part of the deploy pipeline.

• Emphasize idempotence and ordered migrations.

• Provide example steps like:

  1. Run tests.
  2. Build Worker.
  3. Apply migrations to staging DB.
  4. Deploy Worker to staging.
  5. After verification, apply migrations to prod DB.
  6. Deploy Worker to prod.

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Error Handling & Debugging

When migrations fail, this skill should:

• Suggest checking:

  • SQL syntax in failing migration.
  • Whether migration was partially applied.
  • D1 console & Wrangler logs.

• Recommend recovery approaches:

  • Fix the migration and re-run (if it never applied successfully anywhere).
  • If applied partially in dev but not staging/prod, you may create a new corrective migration instead of editing history.

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Interaction with Other Skills

• cloudflare-worker-deployment:
  • This skill plugs into that one’s environment config, aligning D1 names with wrangler.toml.
• hono-d1-integration:
  • That skill defines TypeScript types and query helpers; this one defines schema & migrations these queries rely on.
• hono-authentication:
  • For user/auth tables, this skill defines the underlying D1 schema.
• nestjs-typeorm-integration and other DB skills:
  • Conceptual parallels, but for D1 we stay SQL + D1 APIs, not TypeORM.

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Example Prompts That Should Use This Skill

• “Create initial D1 schema and migrations for users/posts.”
• “Add a new table in D1 and generate a migration.”
• “Set up dev/staging/prod migration commands for D1.”
• “Add seeding for local dev in D1.”
• “Safely migrate a column in a D1 table without losing data.”

For such tasks, rely on this skill to maintain a clean, versioned, and environment-aware D1 schema, keeping prod safe while making development and testing smooth.