I created a small NestJS project with typeorm and mysql

Store the ormconfig in separate file and create a datasource using the orm config

src/db/ormconfig.ts

import { DataSourceOptions, DataSource } from 'typeorm';

export const dataSourceOptions: DataSourceOptions = {
  type: (process.env.TYPE as any) ?? 'mysql',
  host: process.env.DB_HOST,
  port: parseInt(process.env.DB_PORT, 10) ?? 3306,
  username: process.env.DB_USERNAME,
  password: process.env.DB_PASSWORD,
  database: process.env.DB_NAME,
  synchronize: false,
  bigNumberStrings: true,
  multipleStatements: true,
  logging: true,
  entities: ['**/*.entity{ .ts,.js}'],
  migrations: ['dist/db/migrations/*{.ts,.js}'],
  migrationsRun: true,
};

const dataSource = new DataSource(dataSourceOptions);

export default dataSource;

Import the created data source in your app src/app.module.ts

import { Module } from "@nestjs/common";
import { TypeOrmModule } from "@nestjs/typeorm";
import { AppController } from "./app.controller";
import { AppService } from "./app.service";
import { dataSourceOptions } from "./db/ormconfig";

@Module({
  imports: [TypeOrmModule.forRoot(dataSourceOptions)], // data source used here
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

Add scripts in package.json to generate migrations package.json

{
  // deps and dev deps
  "scripts": {
    // other package json scripts
    "typeorm": "npm run build && npx typeorm -d dist/db/ormconfig.js",
    "migration:generate": "npm run typeorm -- migration:generate",
    "migration:run": "npm run typeorm -- migration:run",
    "migration:revert": "npm run typeorm -- migration:revert"
  }
}

Now, all you have to do is consume your scripts to generate migrations. Since we are creating a build to create and run the migrations, your app may not have the context of .env variables. I usually follow these steps for creating a migration

Step 1:

• Create a shell file app-env.sh and add all the .env variables with value

app-env.sh

export NODE_ENV=development
export HOST=0.0.0.0
export PORT=3000
# your other environment variables here

• Populate the environment variables to your shell

source app-env.sh

Step 2: Generate migrations by using the following command

npm run migration:generate -- ./src/db/migrations/YourMigrationNameHere

Step 3: Run the migrations with the following command

npm run migration:run

Step 4 (Optional): If you wanted to revert the applied migration

npm run migration:revert

Please note that unless you close your terminal and start a new terminal, any change in .env will not reflect in the app (since we sourced app-env.sh)