D1 Migration

D1 Migration Workflow

Guided workflow for Cloudflare D1 database migrations using Drizzle ORM.

Standard Migration Flow

1. Generate Migration

pnpm db:generate

This creates a new .sql file in drizzle/ (or your configured migrations directory).

2. Inspect the SQL (CRITICAL)

Always read the generated SQL before applying. Drizzle sometimes generates destructive migrations for simple schema changes.

Red Flag: Table Recreation

If you see this pattern, the migration will likely fail:

CREATE TABLE `my_table_new` (...);
INSERT INTO `my_table_new` SELECT ..., `new_column`, ... FROM `my_table`;
--                                      ^^^ This column doesn't exist in old table!
DROP TABLE `my_table`;
ALTER TABLE `my_table_new` RENAME TO `my_table`;

Cause: Changing a column's default value in Drizzle schema triggers full table recreation. The INSERT SELECT references the new column from the old table.

Fix: If you're only adding new columns (no type/constraint changes on existing columns), simplify to:

ALTER TABLE `my_table` ADD COLUMN `new_column` TEXT DEFAULT 'value';