How do I rename mongoose connections in NestJs - node.js

Question

I am having trouble giving a mongoose database connection a name (so that I can use more than one).
I have separated my database config out into a separate module so that I can import it easily when testing e2e.
My Database Module looks like:
import { Module } from "#nestjs/common";
import { MongooseModule } from "#nestjs/mongoose";
import { DatabaseService } from "./database.service";
#Module({
imports: [
MongooseModule.forRootAsync({
//connectionName: 'database',
useFactory: () => ({ uri: `mongodb://mongoUri` }),
}),
],
providers: [DatabaseService],
exports: [DatabaseService]
})
export class DatabaseModule { };
and my Database Service is:
import { Injectable } from "#nestjs/common";
import { InjectConnection } from "#nestjs/mongoose";
import { Connection } from 'mongoose';
#Injectable()
export class DatabaseService {
constructor(#InjectConnection() private readonly connection: Connection) {}
getDbHandle(): Connection {
return this.connection
}
}
with App Module:
import { Module, NestModule } from '#nestjs/common';
import { AppController } from './app.controller';
import { AppService } from './app.service';
import { MyModule } from './my/my.module';
import { DatabaseModule } from './common/database/database.module';
#Module({
imports: [
MyModule,
DatabaseModule
],
controllers: [AppController],
providers: [AppService],
})
export class AppModule implements NestModule {}
and My Module:
import { Module } from '#nestjs/common';
import { MyService } from '../services/my.service';
import { MyController } from '../controllers/my.controller';
import { MongooseModule } from '#nestjs/mongoose';
import { My } from '../models/my.schema';
#Module({
imports: [
MongooseModule.forFeature([{ name: My.name, schema: MySchema }]) //, 'database'),
],
controllers: [MyController],
providers: [MyService]
})
export class MyModule {}
This all works fine, however if I uncomment the comments (i.e. add a connection name in Database Module and to the import in My Module, I get the error: Nest can't resolve dependencies of the DatabaseService (?). Please make sure that the argument DatabaseConnection at index [0] is available in the DatabaseModule context.
What is it that adding a connection name does to cause this error? And how can I resolve it? Any help greatly appreciated.

Answer 1

Because #InjectConnection() takes an optional parameter which is the name, otherwise some "default" connection will be used.
See the source code here:
export const InjectConnection = (name?: string) =>
Inject(getConnectionToken(name));
https://github.com/nestjs/mongoose/blob/master/lib/common/mongoose.decorators.ts