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- Get Started
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- Reference
4.5.10. Write Migration
In this chapter, you'll learn how to create a migration and write it manually.
What is a Migration?#
A migration is a class created in a TypeScript or JavaScript file under a module's migrations
directory. It has two methods:
- The
up
method reflects changes on the database. - The
down
method reverts the changes made in theup
method.
How to Write a Migration?#
The Medusa CLI tool provides a db:generate command to generate a migration for the specified modules' data models.
Alternatively, you can manually create a migration file under the migrations
directory of your module.
For example:
1import { Migration } from "@mikro-orm/migrations"2 3export class Migration20240702105919 extends Migration {4 5 async up(): Promise<void> {6 this.addSql("create table if not exists \"my_custom\" (\"id\" text not null, \"name\" text not null, \"created_at\" timestamptz not null default now(), \"updated_at\" timestamptz not null default now(), \"deleted_at\" timestamptz null, constraint \"my_custom_pkey\" primary key (\"id\"));")7 }8 9 async down(): Promise<void> {10 this.addSql("drop table if exists \"my_custom\" cascade;")11 }12 13}
The migration's file name should be of the format Migration{YEAR}{MONTH}{DAY}.ts
. The migration class in the file extends the Migration
class imported from @mikro-orm/migrations
.
In the up
and down
method of the migration class, you use the addSql
method provided by MikroORM's Migration
class to run PostgreSQL syntax.
In the example above, the up
method creates the table my_custom
, and the down
method drops the table if the migration is reverted.
Run the Migration#
To run your migration, run the following command:
--skip-links
option.This reflects the changes in the database as implemented in the migration's up
method.
Rollback the Migration#
To rollback or revert the last migration you ran for a module, run the following command:
This rolls back the last ran migration on the Hello Module.
More Database Commands#
To learn more about the Medusa CLI's database commands, refer to this CLI reference.