Installation of MikroORM

01-installation.sh

# using yarn
$ yarn add mikro-orm mongodb # for mongo
$ yarn add mikro-orm mysql2  # for mysql
$ yarn add mikro-orm pg      # for postgresql
$ yarn add mikro-orm sqlite  # for sqlite

# or npm
$ npm i -s mikro-orm mongodb # for mongo
$ npm i -s mikro-orm mysql2  # for mysql
$ npm i -s mikro-orm pg      # for postgresql
$ npm i -s mikro-orm sqlite  # for sqlite

02-tsconfig.json

{
  "compilerOptions": {
    "module": "commonjs",
    "target": "es2017",
    "moduleResolution": "node",
    "declaration": true,
    "strict": true,
    "strictPropertyInitialization": false,
    "experimentalDecorators": true
  }
}

03-initialising.ts

const orm = await MikroORM.init({
  entities: [Author, Book, BookTag],
  dbName: 'my-db-name',
  clientUrl: '...', // defaults to 'mongodb://127.0.0.1:27017' for mongodb driver
  type: 'mongo', // one of 'mysql', 'postgresql', 'sqlite', defaults to 'mongo'
  autoFlush: false, // read more here: https://b4nan.github.io/mikro-orm/unit-of-work/
});

console.log(orm.em); // access EntityManager via `em` property

04-forking-entity-manager.ts

const app = express();

app.use((req, res, next) => {
  req.em = orm.em.fork(); // save the fork to `req` object
});

app.get('/books', async (req, res) => {
  const books = await req.em.find(Book); // use the fork via `req.em`
});

05-providing-request-context.ts

const app = express();

// by providing request context, creating forked EntityManager will be handled automatically
app.use((req, res, next) => {
  RequestContext.create(orm.em, next);
});

@stalniy After few hours of thinking and prototyping, I found a way to get around this and provide the API you suggested. Take a look at mikro-orm/mikro-orm#18 :]

I also removed the need for entitiesDirsTs, using tsconfig.json by default. It is a bit slower but one can still use entitiesDirsTs to make it faster.