NestJS Request Scoped Multitenancy for Multiple Databases

Here's what we ended up doing...

Create a simple, global TenancyModule bound to the request scope:

tenancy.module.ts

import { Global, Module, Scope } from '@nestjs/common';
import { REQUEST } from '@nestjs/core';
import { getConnection } from 'typeorm';

const connectionFactory = {
  provide: 'CONNECTION',
  scope: Scope.REQUEST,
  useFactory: (req) => {
    const tenant = someMethodToDetermineTenantFromHost(req.headers.host);
    return getConnection(tenant);
  },
  inject: [REQUEST],
};

@Global()
@Module({
  providers: [connectionFactory],
  exports: ['CONNECTION'],
})
export class TenancyModule {}

Inject request-specific 'CONNECTION' into module services from which to retrieve repositories:

user.service.ts

...
@Injectable({scope: Scope.REQUEST})
export class UserService {
  private readonly userRepository: Repository<User>;

  constructor(@Inject('CONNECTION') connection) {
    this.userRepository = connection.getRepository(User);
  }

I would recommend to use the approach by @nurikabe with a request scoped factory provider and request scoped services. Nestjs itself has a similar factory example in the docs.

But for the sake of completenes, there is also another approach: You could also use a middleware and attach the connection to the request object as described in this answer to a similar question. However, attaching things like a connection to the request via a middleware is circumventing the DI mechanism and alienates the request object by making it behave like a service container that delivers the connection – therefore the factory approach should be preferred.

NestJS Request Scoped Multitenancy for Multiple Databases

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