migration

name	migration
description	This skill should be used when the user asks to "create a migration", "add a column", "modify the schema", "database migration", or wants to generate a database migration file.
category	operations
argument-hint	<description>

Generate a database migration for: $ARGUMENTS

Detect Migration Framework

1. Identify the ORM and migration tool:

   • Django: manage.py exists, look for migrations/ directories under apps
   • Alembic (SQLAlchemy): alembic.ini or alembic/ directory exists
   • Prisma: prisma/schema.prisma exists
   • Knex: knexfile.js or knexfile.ts exists
   • TypeORM: ormconfig.* or typeorm in package.json
   • Drizzle: drizzle.config.* exists
   • Rails ActiveRecord: db/migrate/ exists
   • Sequelize: sequelize in package.json, .sequelizerc exists

2. If no framework detected, tell the user and stop. Do not generate raw SQL.

Understand Current Schema

3. Read relevant models to understand the current state:

   • Django: find the app's models.py
   • SQLAlchemy: find model files (usually in models/ or models.py)
   • Prisma: read prisma/schema.prisma
   • Rails: read db/schema.rb

4. Read existing migrations (last 3-5) to understand:

   • Naming convention (timestamp prefix, sequential numbers, descriptive names)
   • Import patterns
   • Migration style (auto-generated vs hand-written)
   • Rollback patterns (up/down, reversible)

Generate the Migration

5. For Django:

   • Modify the model in models.py to reflect the desired change
   • Run python manage.py makemigrations to auto-generate
   • Review the generated migration for correctness
   • If auto-generation isn't possible (data migration), write a manual migration following existing patterns

6. For Alembic:

   • Generate with alembic revision --autogenerate -m "$ARGUMENTS" if models are updated
   • Or write a manual migration with alembic revision -m "$ARGUMENTS"
   • Include both upgrade() and downgrade() functions
   • Follow the naming pattern from existing migrations

7. For Prisma:

   • Update prisma/schema.prisma with the new schema
   • Tell the user to run npx prisma migrate dev --name $ARGUMENTS

8. For Knex/TypeORM/Drizzle/Sequelize:

   • Generate migration file following the framework's CLI conventions
   • Include both up and down migrations
   • Match existing migration style

9. For Rails:

   • Generate with rails generate migration $ARGUMENTS
   • Or write manually in db/migrate/ with timestamp prefix

Validate

10. Check the migration for common mistakes:

    • Missing indexes on foreign keys or frequently queried columns
    • Missing NOT NULL constraints with no default value on existing tables (will fail on non-empty tables)
    • Destructive operations (DROP COLUMN, DROP TABLE) without explicit confirmation
    • Missing rollback/down migration

11. Show the migration and the command to run it.

Edge Cases

• No migration framework detected: Suggest the most common framework for the detected language. Do not generate raw SQL.
• Destructive migration (drop column/table): Flag clearly and ask for confirmation. Suggest a multi-step approach (deprecate, then remove).
• Data migration needed: Note that data migrations require careful handling and suggest testing on a copy of production data.
• Multiple apps/modules: Ask which app the migration belongs to if ambiguous.