How to create and use custom middleware?

[Zhuravlev1]

I am trying to implement custom middleware with a connection to DB using Prisma. My AppModule is:

@Module({
  imports: [
    TelegrafModule.forRootAsync({
      imports: [ConfigModule, LoggerModule],
      useFactory: (configService: ConfigService, logger: LoggerMiddleware) => {    
        return {
          token: configService.get<string>("TELEGRAM_TOKEN")!,
          middlewares: [sessionMiddleware, logger.use]
        };
      },
      inject: [ConfigService, LoggerMiddleware]
    }),
    PrismaModule
  ],
  controllers: [],
  providers: [...someProviders]
})
export class AppModule {} 

LoggerMiddleware:

@Injectable()
export class LoggerMiddleware {
  constructor(private readonly prisma: PrismaService) {}

  async use(ctx: Context, next: NextFunction) {
    const listUser = await this.prisma.user.findMany()
    console.log('listUser = ', listUser)
    next()
  }
}

LoggerModule:

@Module({
  imports: [PrismaModule],
  providers: [LoggerMiddleware, PrismaService],
  exports: [LoggerMiddleware]
})
export class LoggerModule {}

It starts without errors and code reaches my logger middleware but then I am getting an error:

TypeError: Cannot read properties of undefined (reading 'prisma')

I have access to Prisma service from another provider and a connection to DB works. At the start, nest initializes all dependencies successfully and returns a result from db if call logger.use({}, () => {}) like this:

useFactory:  async (configService: ConfigService, logger: LoggerMiddleware) => {   
        await logger.use({}, () => {}) // returns a result from DB on server start but failed then when code reaches middleware 
        return {
          token: configService.get<string>("TELEGRAM_TOKEN")!,
          middlewares: [sessionMiddleware, logger.use]
        };
      },

I don't understand why during execution it fell with this error. What did I do wrong? looks like my custom middleware doesn't have dependencies

[evilsprut]

Hey @Zhuravlev1, middlewares it just array of middleware functions in Telegraf module options. Inside the module, we simply take and call bot.use() for each element of the array. In this case, middleware has no Nest dependencies, because they exist outside Nest DI/Ioc.

[Zhuravlev1]

Thnaks! Could you give me some advice how to do it(create a middleware with dependencies)? In fact I try to add telegraf-session-mongodb but i am not sure how to put connection.
I'd appreciate any help.

[evilsprut]

import { Injectable, OnModuleInit } from '@nestjs/common';
import { InjectConnection } from '@nestjs/mongoose';
import { Connection } from 'mongoose';
import { session } from 'telegraf-session-mongodb';
import { InjectBot } from 'nestjs-telegraf'; 

@Injectable()
export class CatsService implements OnModuleInit {
  constructor(@InjectConnection() private connection: Connection, @InjectBot() private bot) {}

  onModuleInit() {
    this.bot.use(session(this.connection.db('main'), { collectionName: 'sessions' }))
  }
}

Something like that, not tested

[evilsprut]

Also you can get bot access in your main.ts file

import { getBotToken } from 'nestjs-telegraf';
import { MongoClient } from 'mongodb';
import { session } from 'telegraf-session-mongodb';

const bot = app.get(getBotToken());

// code from telegram-session-mongodb, should work, but one more connection to DB not good
MongoClient.connect(process.env.MONGODB_URI, { useNewUrlParser: true, useUnifiedTopology: true })
  .then(client => {
    const db = client.db();
    bot.use(session(db, { collectionName: 'sessions' }));
  });

[evilsprut]

Also you can get access to bot in any place, use getBotToken() or @InjectBot(). improvise)