Once you get into production you’ll need to synchronize model changes into the database. Typically, it is unsafe to use synchronize: true for schema synchronization on production once you get data in your database. Here is where migrations come to help.

A migration is just a single file with sql queries to update a database schema and apply new changes to an existing database.

Let’s say you already have a database and a post entity:

import { Entity, Column, PrimaryGeneratedColumn } from "typeorm"

@Entity()
export class Post {
    @PrimaryGeneratedColumn()
    id: number

    @Column()
    title: string

    @Column()
    text: string
}

And your entity worked in production for months without any changes. You have thousands of posts in your database.

Now you need to make a new release and rename title to name. What would you do?

You need to create a new migration with the following MYSQL query :

ALTER TABLE post CHANGE COLUMN name description   VARCHAR(255);

Once you run this SQL query your database schema is ready to work with your new codebase. TypeORM provides a place where you can write such sql queries and run them when needed. This place is called “migrations”.

Creating a new migration

Pre-requisites: Installing CLI

Before creating a new migration you need to setup your data source options properly:

{
    type: "mysql",
    host: "localhost",
    port: 3306,
    username: "test",
    password: "test",
    database: "test",
    entities: [/*...*/],
    migrations: [/*...*/],
    migrationsTableName: "custom_migration_table",
}

Here we setup two options:

• "migrationsTableName": "migrations" – Specify this option only if you need migration table name to be different from "migrations".
• "migrations": [/*...*/] – list of migrations need to be loaded by TypeORM

Once you setup connection options you can create a new migration using CLI:

typeorm migration:create ./path-to-migrations-dir/PostRefactoring

Here, PostRefactoring is the name of the migration – you can specify any name you want. After you run the command you can see a new file generated in the “migration” directory named {TIMESTAMP}-PostRefactoring.ts where {TIMESTAMP} is the current timestamp when the migration was generated. Now you can open the file and add your migration sql queries there.

You should see the following content inside your migration:

import { MigrationInterface, QueryRunner } from "typeorm"

export class PostRefactoringTIMESTAMP implements MigrationInterface {
    async up(queryRunner: QueryRunner): Promise<void> {}

    async down(queryRunner: QueryRunner): Promise<void> {}
}

There are two methods you must fill with your migration code: up and down. up has to contain the code you need to perform the migration. down has to revert whatever up changed. down method is used to revert the last migration.

Inside both up and down you have a QueryRunner object. All database operations are executed using this object. Learn more about query runner.

Let’s see what the migration looks like with our Post changes:

import { MigrationInterface, QueryRunner } from "typeorm"

export class PostRefactoringTIMESTAMP implements MigrationInterface {
    async up(queryRunner: QueryRunner): Promise<void> {
        await queryRunner.query(
            `ALTER TABLE "post" RENAME COLUMN "title" TO "name"`,
        )
    }

    async down(queryRunner: QueryRunner): Promise<void> {
        await queryRunner.query(
            `ALTER TABLE "post" RENAME COLUMN "name" TO "title"`,
        ) // reverts things made in "up" method
    }
}

Running and reverting migrations

Once you have a migration to run on production, you can run them using a CLI command:

typeorm migration:run -- -d path-to-datasource-config

typeorm migration:create and typeorm migration:generate will create .ts files, unless you use the o flag (see more in Generating migrations). The migration:run and migration:revert commands only work on .js files. Thus the typescript files need to be compiled before running the commands. Alternatively you can use ts-node in conjunction with typeorm to run .ts migration files.

Example with ts-node:

npx typeorm-ts-node-commonjs migration:run -- -d path-to-datasource-config

Example with ts-node in ESM projects:

npx typeorm-ts-node-esm migration:run -- -d path-to-datasource-config

npx typeorm-ts-node-esm migration:generate ./src/migrations/update-post-table -d ./src/data-source.ts

This command will execute all pending migrations and run them in a sequence ordered by their timestamps. This means all sql queries written in the up methods of your created migrations will be executed. That’s all! Now you have your database schema up-to-date.

If for some reason you want to revert the changes, you can run:

typeorm migration:revert -- -d path-to-datasource-config

This command will execute down in the latest executed migration. If you need to revert multiple migrations you must call this command multiple times.

Faking Migrations and Rollbacks

You can also fake run a migration using the --fake flag (-f for short). This will add the migration to the migrations table without running it. This is useful for migrations created after manual changes have already been made to the database or when migrations have been run externally (e.g. by another tool or application), and you still would like to keep a consistent migration history.

typeorm migration:run --fake

This is also possible with rollbacks.

typeorm migration:revert --fake